KASAN: use-after-free Write in snd_rawmidi_kernel_write1
I report a bug (in linux-5.7-rc1) found by syzkaller. kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.7.0-rc1.confi... reproducer: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/repro.cprog I test the reproducer in linux-5.7-rc4 and crash too. crash log: ================================================================== BUG: KASAN: use-after-free in _copy_from_user+0x113/0x1a0 lib/usercopy.c:13 Write of size 1 at addr ffff888069da43ca by task syz-executor611/6797 CPU: 0 PID: 6797 Comm: syz-executor611 Not tainted 5.7.0-rc1 #3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x188/0x20d lib/dump_stack.c:118 print_address_description.constprop.0.cold+0xd3/0x347 mm/kasan/report.c:382 __kasan_report.cold+0x35/0x4d mm/kasan/report.c:511 kasan_report+0x33/0x50 mm/kasan/common.c:625 check_memory_region_inline mm/kasan/generic.c:187 [inline] check_memory_region+0x141/0x190 mm/kasan/generic.c:193 _copy_from_user+0x113/0x1a0 lib/usercopy.c:13 copy_from_user include/linux/uaccess.h:144 [inline] snd_rawmidi_kernel_write1+0x320/0x6f0 sound/core/rawmidi.c:1363 snd_rawmidi_write+0x2e4/0xb80 sound/core/rawmidi.c:1429 __vfs_write+0x76/0x100 fs/read_write.c:495 vfs_write+0x268/0x5d0 fs/read_write.c:559 ksys_write+0x1ee/0x250 fs/read_write.c:612 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 RIP: 0033:0x4553a9 Code: 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f556b7f5cc8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00000000006d9588 RCX: 00000000004553a9 RDX: 00000000fffffc85 RSI: 0000000020000040 RDI: 0000000000000004 RBP: 00000000006d9580 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006d958c R13: 0000000000000000 R14: 00000000006d9580 R15: 00007fff34bcb390 Allocated by task 6797: save_stack+0x1b/0x40 mm/kasan/common.c:49 set_track mm/kasan/common.c:57 [inline] __kasan_kmalloc mm/kasan/common.c:495 [inline] __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:468 kmalloc_node include/linux/slab.h:578 [inline] kvmalloc_node+0x61/0xf0 mm/util.c:574 kvmalloc include/linux/mm.h:757 [inline] kvzalloc include/linux/mm.h:765 [inline] snd_rawmidi_runtime_create sound/core/rawmidi.c:141 [inline] open_substream+0x33d/0x880 sound/core/rawmidi.c:285 rawmidi_open_priv+0x58e/0x6e0 sound/core/rawmidi.c:336 snd_rawmidi_open+0x455/0xb20 sound/core/rawmidi.c:433 snd_open+0x212/0x3d0 sound/core/sound.c:163 chrdev_open+0x219/0x5c0 fs/char_dev.c:414 do_dentry_open+0x4ba/0x1290 fs/open.c:797 do_open fs/namei.c:3229 [inline] path_openat+0x1e59/0x27d0 fs/namei.c:3346 do_filp_open+0x192/0x260 fs/namei.c:3373 do_sys_openat2+0x585/0x7d0 fs/open.c:1148 do_sys_open+0xc3/0x140 fs/open.c:1164 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 Freed by task 6798: save_stack+0x1b/0x40 mm/kasan/common.c:49 set_track mm/kasan/common.c:57 [inline] kasan_set_free_info mm/kasan/common.c:317 [inline] __kasan_slab_free+0x126/0x170 mm/kasan/common.c:456 slab_free_hook mm/slub.c:1445 [inline] slab_free_freelist_hook+0xc4/0x1c0 mm/slub.c:1478 slab_free mm/slub.c:3035 [inline] kfree+0xd8/0x330 mm/slub.c:4003 kvfree+0x42/0x50 mm/util.c:603 resize_runtime_buffer+0x29e/0x370 sound/core/rawmidi.c:677 snd_rawmidi_output_params+0x128/0x170 sound/core/rawmidi.c:690 snd_rawmidi_ioctl+0x544/0x5b0 sound/core/rawmidi.c:841 vfs_ioctl fs/ioctl.c:47 [inline] ksys_ioctl+0x11a/0x180 fs/ioctl.c:763 __do_sys_ioctl fs/ioctl.c:772 [inline] __se_sys_ioctl fs/ioctl.c:770 [inline] __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:770 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 The buggy address belongs to the object at ffff888069da4000 which belongs to the cache kmalloc-4k of size 4096 The buggy address is located 970 bytes inside of 4096-byte region [ffff888069da4000, ffff888069da5000) The buggy address belongs to the page: page:ffffea0001a76800 refcount:1 mapcount:0 mapping:00000000c136e8e7 index:0x0 head:ffffea0001a76800 order:3 compound_mapcount:0 compound_pincount:0 flags: 0xfffe0000010200(slab|head) raw: 00fffe0000010200 dead000000000100 dead000000000122 ffff88806bc0c280 raw: 0000000000000000 0000000080040004 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff888069da4280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888069da4300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888069da4380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888069da4400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888069da4480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================
Regards, butt3rflyh4ck
On Thu, May 07, 2020 at 04:04:25PM +0800, butt3rflyh4ck wrote:
I report a bug (in linux-5.7-rc1) found by syzkaller.
kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.7.0-rc1.confi... reproducer: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/repro.cprog
I test the reproducer in linux-5.7-rc4 and crash too.
Great, care to create a fix for this and send it to the proper maintainers? That's the best way to get it fixed, otherwise it just goes in the file with the rest of the syzbot reports we are burried under. thanks, greg k-h
On Thu, 07 May 2020 10:23:02 +0200, Greg Kroah-Hartman wrote:
On Thu, May 07, 2020 at 04:04:25PM +0800, butt3rflyh4ck wrote:
I report a bug (in linux-5.7-rc1) found by syzkaller.
kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.7.0-rc1.confi... reproducer: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/repro.cprog
I test the reproducer in linux-5.7-rc4 and crash too.
Great, care to create a fix for this and send it to the proper maintainers? That's the best way to get it fixed, otherwise it just goes in the file with the rest of the syzbot reports we are burried under.
Don't worry, I already prepared a fix patch below :) thanks, Takashi -- 8< -- From: Takashi Iwai <tiwai@suse.de> Subject: [PATCH] ALSA: rawmidi: Fix racy buffer resize under concurrent accesses The rawmidi core allows user to resize the runtime buffer via ioctl, and this may lead to UAF when performed during concurrent reads or writes. This patch fixes the race by introducing a reference counter for the runtime buffer access and returns -EBUSY error when the resize is performed concurrently. Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAFcO6XMWpUVK_yzzCpp8_XP7+=oUpQvuBeCbMffEDkpe8jWrf... Signed-off-by: Takashi Iwai <tiwai@suse.de> --- include/sound/rawmidi.h | 1 + sound/core/rawmidi.c | 29 ++++++++++++++++++++++++++++- 2 files changed, 29 insertions(+), 1 deletion(-) diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h index a36b7227a15a..334842daa904 100644 --- a/include/sound/rawmidi.h +++ b/include/sound/rawmidi.h @@ -61,6 +61,7 @@ struct snd_rawmidi_runtime { size_t avail_min; /* min avail for wakeup */ size_t avail; /* max used buffer for wakeup */ size_t xruns; /* over/underruns counter */ + int buffer_ref; /* buffer reference count */ /* misc */ spinlock_t lock; wait_queue_head_t sleep; diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c index 20dd08e1f675..4185d9e81e3c 100644 --- a/sound/core/rawmidi.c +++ b/sound/core/rawmidi.c @@ -120,6 +120,17 @@ static void snd_rawmidi_input_event_work(struct work_struct *work) runtime->event(runtime->substream); } +/* buffer refcount management: call with runtime->lock held */ +static inline void snd_rawmidi_buffer_ref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref++; +} + +static inline void snd_rawmidi_buffer_unref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref--; +} + static int snd_rawmidi_runtime_create(struct snd_rawmidi_substream *substream) { struct snd_rawmidi_runtime *runtime; @@ -669,6 +680,11 @@ static int resize_runtime_buffer(struct snd_rawmidi_runtime *runtime, if (!newbuf) return -ENOMEM; spin_lock_irq(&runtime->lock); + if (runtime->buffer_ref) { + spin_unlock_irq(&runtime->lock); + kvfree(newbuf); + return -EBUSY; + } oldbuf = runtime->buffer; runtime->buffer = newbuf; runtime->buffer_size = params->buffer_size; @@ -962,6 +978,7 @@ int snd_rawmidi_receive(struct snd_rawmidi_substream *substream, return -EINVAL; } spin_lock_irqsave(&runtime->lock, flags); + snd_rawmidi_buffer_ref(runtime); if (count == 1) { /* special case, faster code */ substream->bytes++; if (runtime->avail < runtime->buffer_size) { @@ -1006,6 +1023,7 @@ int snd_rawmidi_receive(struct snd_rawmidi_substream *substream, else if (snd_rawmidi_ready(substream)) wake_up(&runtime->sleep); } + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags); return result; } @@ -1021,6 +1039,7 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, unsigned long appl_ptr; spin_lock_irqsave(&runtime->lock, flags); + snd_rawmidi_buffer_ref(runtime); while (count > 0 && runtime->avail) { count1 = runtime->buffer_size - runtime->appl_ptr; if (count1 > count) @@ -1040,13 +1059,17 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, spin_unlock_irqrestore(&runtime->lock, flags); if (copy_to_user(userbuf + result, runtime->buffer + appl_ptr, count1)) { - return result > 0 ? result : -EFAULT; + if (!result) + result = -EFAULT; + goto out; } spin_lock_irqsave(&runtime->lock, flags); } result += count1; count -= count1; } + out: + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags); return result; } @@ -1156,6 +1179,7 @@ int __snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, return -EINVAL; } result = 0; + snd_rawmidi_buffer_ref(runtime); if (runtime->avail >= runtime->buffer_size) { /* warning: lowlevel layer MUST trigger down the hardware */ goto __skip; @@ -1180,6 +1204,7 @@ int __snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, } } __skip: + snd_rawmidi_buffer_unref(runtime); return result; } EXPORT_SYMBOL(__snd_rawmidi_transmit_peek); @@ -1342,6 +1367,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream, return -EAGAIN; } } + snd_rawmidi_buffer_ref(runtime); while (count > 0 && runtime->avail > 0) { count1 = runtime->buffer_size - runtime->appl_ptr; if (count1 > count) @@ -1373,6 +1399,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream, } __end: count1 = runtime->avail < runtime->buffer_size; + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags); if (count1) snd_rawmidi_output_trigger(substream, 1); -- 2.25.0
On Thu, May 07, 2020 at 11:56:22AM +0200, Takashi Iwai wrote:
On Thu, 07 May 2020 10:23:02 +0200, Greg Kroah-Hartman wrote:
On Thu, May 07, 2020 at 04:04:25PM +0800, butt3rflyh4ck wrote:
I report a bug (in linux-5.7-rc1) found by syzkaller.
kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.7.0-rc1.confi... reproducer: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/repro.cprog
I test the reproducer in linux-5.7-rc4 and crash too.
Great, care to create a fix for this and send it to the proper maintainers? That's the best way to get it fixed, otherwise it just goes in the file with the rest of the syzbot reports we are burried under.
Don't worry, I already prepared a fix patch below :)
thanks,
Takashi
-- 8< -- From: Takashi Iwai <tiwai@suse.de> Subject: [PATCH] ALSA: rawmidi: Fix racy buffer resize under concurrent accesses
The rawmidi core allows user to resize the runtime buffer via ioctl, and this may lead to UAF when performed during concurrent reads or writes.
This patch fixes the race by introducing a reference counter for the runtime buffer access and returns -EBUSY error when the resize is performed concurrently.
Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAFcO6XMWpUVK_yzzCpp8_XP7+=oUpQvuBeCbMffEDkpe8jWrf... Signed-off-by: Takashi Iwai <tiwai@suse.de> --- include/sound/rawmidi.h | 1 + sound/core/rawmidi.c | 29 ++++++++++++++++++++++++++++- 2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h index a36b7227a15a..334842daa904 100644 --- a/include/sound/rawmidi.h +++ b/include/sound/rawmidi.h @@ -61,6 +61,7 @@ struct snd_rawmidi_runtime { size_t avail_min; /* min avail for wakeup */ size_t avail; /* max used buffer for wakeup */ size_t xruns; /* over/underruns counter */ + int buffer_ref; /* buffer reference count */ /* misc */ spinlock_t lock; wait_queue_head_t sleep; diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c index 20dd08e1f675..4185d9e81e3c 100644 --- a/sound/core/rawmidi.c +++ b/sound/core/rawmidi.c @@ -120,6 +120,17 @@ static void snd_rawmidi_input_event_work(struct work_struct *work) runtime->event(runtime->substream); }
+/* buffer refcount management: call with runtime->lock held */ +static inline void snd_rawmidi_buffer_ref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref++; +} + +static inline void snd_rawmidi_buffer_unref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref--; +}
Why not use the reference count structure? greg k-h
On Thu, 07 May 2020 12:13:10 +0200, Greg Kroah-Hartman wrote:
On Thu, May 07, 2020 at 11:56:22AM +0200, Takashi Iwai wrote:
On Thu, 07 May 2020 10:23:02 +0200, Greg Kroah-Hartman wrote:
On Thu, May 07, 2020 at 04:04:25PM +0800, butt3rflyh4ck wrote:
I report a bug (in linux-5.7-rc1) found by syzkaller.
kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.7.0-rc1.confi... reproducer: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/repro.cprog
I test the reproducer in linux-5.7-rc4 and crash too.
Great, care to create a fix for this and send it to the proper maintainers? That's the best way to get it fixed, otherwise it just goes in the file with the rest of the syzbot reports we are burried under.
Don't worry, I already prepared a fix patch below :)
thanks,
Takashi
-- 8< -- From: Takashi Iwai <tiwai@suse.de> Subject: [PATCH] ALSA: rawmidi: Fix racy buffer resize under concurrent accesses
The rawmidi core allows user to resize the runtime buffer via ioctl, and this may lead to UAF when performed during concurrent reads or writes.
This patch fixes the race by introducing a reference counter for the runtime buffer access and returns -EBUSY error when the resize is performed concurrently.
Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAFcO6XMWpUVK_yzzCpp8_XP7+=oUpQvuBeCbMffEDkpe8jWrf... Signed-off-by: Takashi Iwai <tiwai@suse.de> --- include/sound/rawmidi.h | 1 + sound/core/rawmidi.c | 29 ++++++++++++++++++++++++++++- 2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h index a36b7227a15a..334842daa904 100644 --- a/include/sound/rawmidi.h +++ b/include/sound/rawmidi.h @@ -61,6 +61,7 @@ struct snd_rawmidi_runtime { size_t avail_min; /* min avail for wakeup */ size_t avail; /* max used buffer for wakeup */ size_t xruns; /* over/underruns counter */ + int buffer_ref; /* buffer reference count */ /* misc */ spinlock_t lock; wait_queue_head_t sleep; diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c index 20dd08e1f675..4185d9e81e3c 100644 --- a/sound/core/rawmidi.c +++ b/sound/core/rawmidi.c @@ -120,6 +120,17 @@ static void snd_rawmidi_input_event_work(struct work_struct *work) runtime->event(runtime->substream); }
+/* buffer refcount management: call with runtime->lock held */ +static inline void snd_rawmidi_buffer_ref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref++; +} + +static inline void snd_rawmidi_buffer_unref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref--; +}
Why not use the reference count structure?
The context accessing the buffer is always with the spinlock, so we don't need expensive atomic ops there. Usually this kind of check can be a simple boolean flag, but in this case, there is one place that goes out of lock due to copy_from/to_user, so a refcount is used in this patch instead. thanks, Takashi
On Thu, May 07, 2020 at 12:19:18PM +0200, Takashi Iwai wrote:
On Thu, 07 May 2020 12:13:10 +0200, Greg Kroah-Hartman wrote:
On Thu, May 07, 2020 at 11:56:22AM +0200, Takashi Iwai wrote:
On Thu, 07 May 2020 10:23:02 +0200, Greg Kroah-Hartman wrote:
On Thu, May 07, 2020 at 04:04:25PM +0800, butt3rflyh4ck wrote:
I report a bug (in linux-5.7-rc1) found by syzkaller.
kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.7.0-rc1.confi... reproducer: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/repro.cprog
I test the reproducer in linux-5.7-rc4 and crash too.
Great, care to create a fix for this and send it to the proper maintainers? That's the best way to get it fixed, otherwise it just goes in the file with the rest of the syzbot reports we are burried under.
Don't worry, I already prepared a fix patch below :)
thanks,
Takashi
-- 8< -- From: Takashi Iwai <tiwai@suse.de> Subject: [PATCH] ALSA: rawmidi: Fix racy buffer resize under concurrent accesses
The rawmidi core allows user to resize the runtime buffer via ioctl, and this may lead to UAF when performed during concurrent reads or writes.
This patch fixes the race by introducing a reference counter for the runtime buffer access and returns -EBUSY error when the resize is performed concurrently.
Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAFcO6XMWpUVK_yzzCpp8_XP7+=oUpQvuBeCbMffEDkpe8jWrf... Signed-off-by: Takashi Iwai <tiwai@suse.de> --- include/sound/rawmidi.h | 1 + sound/core/rawmidi.c | 29 ++++++++++++++++++++++++++++- 2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h index a36b7227a15a..334842daa904 100644 --- a/include/sound/rawmidi.h +++ b/include/sound/rawmidi.h @@ -61,6 +61,7 @@ struct snd_rawmidi_runtime { size_t avail_min; /* min avail for wakeup */ size_t avail; /* max used buffer for wakeup */ size_t xruns; /* over/underruns counter */ + int buffer_ref; /* buffer reference count */ /* misc */ spinlock_t lock; wait_queue_head_t sleep; diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c index 20dd08e1f675..4185d9e81e3c 100644 --- a/sound/core/rawmidi.c +++ b/sound/core/rawmidi.c @@ -120,6 +120,17 @@ static void snd_rawmidi_input_event_work(struct work_struct *work) runtime->event(runtime->substream); }
+/* buffer refcount management: call with runtime->lock held */ +static inline void snd_rawmidi_buffer_ref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref++; +} + +static inline void snd_rawmidi_buffer_unref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref--; +}
Why not use the reference count structure?
The context accessing the buffer is always with the spinlock, so we don't need expensive atomic ops there.
Usually this kind of check can be a simple boolean flag, but in this case, there is one place that goes out of lock due to copy_from/to_user, so a refcount is used in this patch instead.
Ah, ok, thanks for the explanation. greg k-h
On 5/7/2020 11:56 AM, Takashi Iwai wrote:
On Thu, 07 May 2020 10:23:02 +0200, Greg Kroah-Hartman wrote:
On Thu, May 07, 2020 at 04:04:25PM +0800, butt3rflyh4ck wrote:
I report a bug (in linux-5.7-rc1) found by syzkaller.
kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.7.0-rc1.confi... reproducer: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/repro.cprog
I test the reproducer in linux-5.7-rc4 and crash too.
Great, care to create a fix for this and send it to the proper maintainers? That's the best way to get it fixed, otherwise it just goes in the file with the rest of the syzbot reports we are burried under.
Don't worry, I already prepared a fix patch below :)
thanks,
Takashi
-- 8< -- From: Takashi Iwai <tiwai@suse.de> Subject: [PATCH] ALSA: rawmidi: Fix racy buffer resize under concurrent accesses
The rawmidi core allows user to resize the runtime buffer via ioctl, and this may lead to UAF when performed during concurrent reads or writes.
This patch fixes the race by introducing a reference counter for the runtime buffer access and returns -EBUSY error when the resize is performed concurrently.
Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAFcO6XMWpUVK_yzzCpp8_XP7+=oUpQvuBeCbMffEDkpe8jWrf... Signed-off-by: Takashi Iwai <tiwai@suse.de> --- include/sound/rawmidi.h | 1 + sound/core/rawmidi.c | 29 ++++++++++++++++++++++++++++- 2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h index a36b7227a15a..334842daa904 100644 --- a/include/sound/rawmidi.h
(...)
@@ -1021,6 +1039,7 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, unsigned long appl_ptr;
spin_lock_irqsave(&runtime->lock, flags); + snd_rawmidi_buffer_ref(runtime); while (count > 0 && runtime->avail) { count1 = runtime->buffer_size - runtime->appl_ptr; if (count1 > count) @@ -1040,13 +1059,17 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, spin_unlock_irqrestore(&runtime->lock, flags); First unlock if (copy_to_user(userbuf + result, runtime->buffer + appl_ptr, count1)) { - return result > 0 ? result : -EFAULT; + if (!result) + result = -EFAULT; + goto out;
goto -> Second unlock
} spin_lock_irqsave(&runtime->lock, flags); } result += count1; count -= count1; } + out: + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags);
Second unlock
return result; }
So if I follow this correctly, you call spin_unlock_irqrestore twice in case of error?
On Thu, 07 May 2020 12:27:41 +0200, Amadeusz SX2awiX4ski wrote:
On 5/7/2020 11:56 AM, Takashi Iwai wrote:
On Thu, 07 May 2020 10:23:02 +0200, Greg Kroah-Hartman wrote:
On Thu, May 07, 2020 at 04:04:25PM +0800, butt3rflyh4ck wrote:
I report a bug (in linux-5.7-rc1) found by syzkaller.
kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.7.0-rc1.confi... reproducer: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/repro.cprog
I test the reproducer in linux-5.7-rc4 and crash too.
Great, care to create a fix for this and send it to the proper maintainers? That's the best way to get it fixed, otherwise it just goes in the file with the rest of the syzbot reports we are burried under.
Don't worry, I already prepared a fix patch below :)
thanks,
Takashi
-- 8< -- From: Takashi Iwai <tiwai@suse.de> Subject: [PATCH] ALSA: rawmidi: Fix racy buffer resize under concurrent accesses
The rawmidi core allows user to resize the runtime buffer via ioctl, and this may lead to UAF when performed during concurrent reads or writes.
This patch fixes the race by introducing a reference counter for the runtime buffer access and returns -EBUSY error when the resize is performed concurrently.
Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAFcO6XMWpUVK_yzzCpp8_XP7+=oUpQvuBeCbMffEDkpe8jWrf... Signed-off-by: Takashi Iwai <tiwai@suse.de> --- include/sound/rawmidi.h | 1 + sound/core/rawmidi.c | 29 ++++++++++++++++++++++++++++- 2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h index a36b7227a15a..334842daa904 100644 --- a/include/sound/rawmidi.h
(...)
@@ -1021,6 +1039,7 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, unsigned long appl_ptr; spin_lock_irqsave(&runtime->lock, flags); + snd_rawmidi_buffer_ref(runtime); while (count > 0 && runtime->avail) { count1 = runtime->buffer_size - runtime->appl_ptr; if (count1 > count) @@ -1040,13 +1059,17 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, spin_unlock_irqrestore(&runtime->lock, flags); First unlock if (copy_to_user(userbuf + result, runtime->buffer + appl_ptr, count1)) { - return result > 0 ? result : -EFAULT; + if (!result) + result = -EFAULT; + goto out;
goto -> Second unlock
} spin_lock_irqsave(&runtime->lock, flags); } result += count1; count -= count1; } + out: + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags);
Second unlock
return result; }
So if I follow this correctly, you call spin_unlock_irqrestore twice in case of error?
Erm no, this is obviously wrong. The error path needs re-lock. Will respin the fix. thanks, Takashi
On Thu, 07 May 2020 12:36:14 +0200, Takashi Iwai wrote:
On Thu, 07 May 2020 12:27:41 +0200, Amadeusz SX2awiX4ski wrote:
So if I follow this correctly, you call spin_unlock_irqrestore twice in case of error?
Erm no, this is obviously wrong. The error path needs re-lock. Will respin the fix.
... and below is the revised patch. Takashi -- 8< -- From: Takashi Iwai <tiwai@suse.de> Subject: [PATCH v2] ALSA: rawmidi: Fix racy buffer resize under concurrent accesses The rawmidi core allows user to resize the runtime buffer via ioctl, and this may lead to UAF when performed during concurrent reads or writes. This patch fixes the race by introducing a reference counter for the runtime buffer access and returns -EBUSY error when the resize is performed concurrently. Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAFcO6XMWpUVK_yzzCpp8_XP7+=oUpQvuBeCbMffEDkpe8jWrf... Signed-off-by: Takashi Iwai <tiwai@suse.de> --- v1->v2: Fix spinlock unbalance at error path of snd_rawmidi_kernel_read1() include/sound/rawmidi.h | 1 + sound/core/rawmidi.c | 35 +++++++++++++++++++++++++++++++---- 2 files changed, 32 insertions(+), 4 deletions(-) diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h index a36b7227a15a..334842daa904 100644 --- a/include/sound/rawmidi.h +++ b/include/sound/rawmidi.h @@ -61,6 +61,7 @@ struct snd_rawmidi_runtime { size_t avail_min; /* min avail for wakeup */ size_t avail; /* max used buffer for wakeup */ size_t xruns; /* over/underruns counter */ + int buffer_ref; /* buffer reference count */ /* misc */ spinlock_t lock; wait_queue_head_t sleep; diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c index 20dd08e1f675..d9f20dd990db 100644 --- a/sound/core/rawmidi.c +++ b/sound/core/rawmidi.c @@ -120,6 +120,17 @@ static void snd_rawmidi_input_event_work(struct work_struct *work) runtime->event(runtime->substream); } +/* buffer refcount management: call with runtime->lock held */ +static inline void snd_rawmidi_buffer_ref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref++; +} + +static inline void snd_rawmidi_buffer_unref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref--; +} + static int snd_rawmidi_runtime_create(struct snd_rawmidi_substream *substream) { struct snd_rawmidi_runtime *runtime; @@ -669,6 +680,11 @@ static int resize_runtime_buffer(struct snd_rawmidi_runtime *runtime, if (!newbuf) return -ENOMEM; spin_lock_irq(&runtime->lock); + if (runtime->buffer_ref) { + spin_unlock_irq(&runtime->lock); + kvfree(newbuf); + return -EBUSY; + } oldbuf = runtime->buffer; runtime->buffer = newbuf; runtime->buffer_size = params->buffer_size; @@ -962,6 +978,7 @@ int snd_rawmidi_receive(struct snd_rawmidi_substream *substream, return -EINVAL; } spin_lock_irqsave(&runtime->lock, flags); + snd_rawmidi_buffer_ref(runtime); if (count == 1) { /* special case, faster code */ substream->bytes++; if (runtime->avail < runtime->buffer_size) { @@ -1006,6 +1023,7 @@ int snd_rawmidi_receive(struct snd_rawmidi_substream *substream, else if (snd_rawmidi_ready(substream)) wake_up(&runtime->sleep); } + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags); return result; } @@ -1019,8 +1037,10 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, long result = 0, count1; struct snd_rawmidi_runtime *runtime = substream->runtime; unsigned long appl_ptr; + int err = 0; spin_lock_irqsave(&runtime->lock, flags); + snd_rawmidi_buffer_ref(runtime); while (count > 0 && runtime->avail) { count1 = runtime->buffer_size - runtime->appl_ptr; if (count1 > count) @@ -1039,16 +1059,19 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, if (userbuf) { spin_unlock_irqrestore(&runtime->lock, flags); if (copy_to_user(userbuf + result, - runtime->buffer + appl_ptr, count1)) { - return result > 0 ? result : -EFAULT; - } + runtime->buffer + appl_ptr, count1)) + err = -EFAULT; spin_lock_irqsave(&runtime->lock, flags); + if (err) + goto out; } result += count1; count -= count1; } + out: + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags); - return result; + return result > 0 ? result : err; } long snd_rawmidi_kernel_read(struct snd_rawmidi_substream *substream, @@ -1156,6 +1179,7 @@ int __snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, return -EINVAL; } result = 0; + snd_rawmidi_buffer_ref(runtime); if (runtime->avail >= runtime->buffer_size) { /* warning: lowlevel layer MUST trigger down the hardware */ goto __skip; @@ -1180,6 +1204,7 @@ int __snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, } } __skip: + snd_rawmidi_buffer_unref(runtime); return result; } EXPORT_SYMBOL(__snd_rawmidi_transmit_peek); @@ -1342,6 +1367,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream, return -EAGAIN; } } + snd_rawmidi_buffer_ref(runtime); while (count > 0 && runtime->avail > 0) { count1 = runtime->buffer_size - runtime->appl_ptr; if (count1 > count) @@ -1373,6 +1399,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream, } __end: count1 = runtime->avail < runtime->buffer_size; + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags); if (count1) snd_rawmidi_output_trigger(substream, 1); -- 2.25.0
On Thu, 07 May 2020 12:42:27 +0200, Takashi Iwai wrote:
On Thu, 07 May 2020 12:36:14 +0200, Takashi Iwai wrote:
On Thu, 07 May 2020 12:27:41 +0200, Amadeusz SX2awiX4ski wrote:
So if I follow this correctly, you call spin_unlock_irqrestore twice in case of error?
Erm no, this is obviously wrong. The error path needs re-lock. Will respin the fix.
... and below is the revised patch.
and yet more brush up, with a slightly better description. This seems working on my local machine, but let me know if something still goes wrong. thanks, Takashi -- 8< -- From: Takashi Iwai <tiwai@suse.de> Subject: [PATCH v3] ALSA: rawmidi: Fix racy buffer resize under concurrent accesses The rawmidi core allows user to resize the runtime buffer via ioctl, and this may lead to UAF when performed during concurrent reads or writes: the read/write functions unlock the runtime lock temporarily during copying form/to user-space, and that's the race window. This patch fixes the hole by introducing a reference counter for the runtime buffer read/write access and returns -EBUSY error when the resize is performed concurrently against read/write. Note that the ref count field is a simple integer instead of refcount_t here, since the all contexts accessing the buffer is basically protected with a spinlock, hence we need no expensive atomic ops. Also, note that this busy check is needed only against read / write functions, and not in receive/transmit callbacks; the race can happen only at the spinlock hole mentioned in the above, while the whole function is protected for receive / transmit callbacks. Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAFcO6XMWpUVK_yzzCpp8_XP7+=oUpQvuBeCbMffEDkpe8jWrf... Signed-off-by: Takashi Iwai <tiwai@suse.de> --- v1->v2: Fix spinlock unbalance at error path of snd_rawmidi_kernel_read1() v2->v3: Remove superfluous ref in receive/transmit; more detailed patch description include/sound/rawmidi.h | 1 + sound/core/rawmidi.c | 31 +++++++++++++++++++++++++++---- 2 files changed, 28 insertions(+), 4 deletions(-) diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h index a36b7227a15a..334842daa904 100644 --- a/include/sound/rawmidi.h +++ b/include/sound/rawmidi.h @@ -61,6 +61,7 @@ struct snd_rawmidi_runtime { size_t avail_min; /* min avail for wakeup */ size_t avail; /* max used buffer for wakeup */ size_t xruns; /* over/underruns counter */ + int buffer_ref; /* buffer reference count */ /* misc */ spinlock_t lock; wait_queue_head_t sleep; diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c index 20dd08e1f675..2a688b711a9a 100644 --- a/sound/core/rawmidi.c +++ b/sound/core/rawmidi.c @@ -120,6 +120,17 @@ static void snd_rawmidi_input_event_work(struct work_struct *work) runtime->event(runtime->substream); } +/* buffer refcount management: call with runtime->lock held */ +static inline void snd_rawmidi_buffer_ref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref++; +} + +static inline void snd_rawmidi_buffer_unref(struct snd_rawmidi_runtime *runtime) +{ + runtime->buffer_ref--; +} + static int snd_rawmidi_runtime_create(struct snd_rawmidi_substream *substream) { struct snd_rawmidi_runtime *runtime; @@ -669,6 +680,11 @@ static int resize_runtime_buffer(struct snd_rawmidi_runtime *runtime, if (!newbuf) return -ENOMEM; spin_lock_irq(&runtime->lock); + if (runtime->buffer_ref) { + spin_unlock_irq(&runtime->lock); + kvfree(newbuf); + return -EBUSY; + } oldbuf = runtime->buffer; runtime->buffer = newbuf; runtime->buffer_size = params->buffer_size; @@ -1019,8 +1035,10 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, long result = 0, count1; struct snd_rawmidi_runtime *runtime = substream->runtime; unsigned long appl_ptr; + int err = 0; spin_lock_irqsave(&runtime->lock, flags); + snd_rawmidi_buffer_ref(runtime); while (count > 0 && runtime->avail) { count1 = runtime->buffer_size - runtime->appl_ptr; if (count1 > count) @@ -1039,16 +1057,19 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream, if (userbuf) { spin_unlock_irqrestore(&runtime->lock, flags); if (copy_to_user(userbuf + result, - runtime->buffer + appl_ptr, count1)) { - return result > 0 ? result : -EFAULT; - } + runtime->buffer + appl_ptr, count1)) + err = -EFAULT; spin_lock_irqsave(&runtime->lock, flags); + if (err) + goto out; } result += count1; count -= count1; } + out: + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags); - return result; + return result > 0 ? result : err; } long snd_rawmidi_kernel_read(struct snd_rawmidi_substream *substream, @@ -1342,6 +1363,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream, return -EAGAIN; } } + snd_rawmidi_buffer_ref(runtime); while (count > 0 && runtime->avail > 0) { count1 = runtime->buffer_size - runtime->appl_ptr; if (count1 > count) @@ -1373,6 +1395,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream, } __end: count1 = runtime->avail < runtime->buffer_size; + snd_rawmidi_buffer_unref(runtime); spin_unlock_irqrestore(&runtime->lock, flags); if (count1) snd_rawmidi_output_trigger(substream, 1); -- 2.25.0
participants (4)
-
Amadeusz Sławiński -
butt3rflyh4ck -
Greg Kroah-Hartman -
Takashi Iwai