On Tue, 02 Feb 2016 22:59:49 +0100, Dmitry Vyukov wrote:
On Mon, Feb 1, 2016 at 12:55 PM, Takashi Iwai tiwai@suse.de wrote:
On Mon, 01 Feb 2016 12:31:20 +0100, Dmitry Vyukov wrote:
Hello,
The following program triggers a splash of WARNINGs in rawmidi_transmit_ack. Takashi, I am on commit 36f90b0a2ddd60823fe193a85e60ff1906c2a9b3 + a bunch of your recent fixes: https://gist.githubusercontent.com/dvyukov/40640128a433ad16a56a/raw/ab3a0863...
Ouch, this is another spot with an open race between snd_rawmidi_transmit_peek() and snd_rawmidi_transmit_ack().
Could you drop the previous fix and apply the one below instead?
FWIW, I pushed sound.git tree topic/core-fixes branch containing all pending fixes. This should be pullable cleanly onto 4.5-rc1/rc2.
git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git topic/core-fixes
Thanks!
Takashi
Now this program hangs the machine with:
Mea culpa, the spinlock was applied at the wrong place. Below is the revised patch. I updated topic/core-fixes branch as well.
thanks,
Takashi
-- 8< -- From: Takashi Iwai tiwai@suse.de Subject: [PATCH v2] ALSA: rawmidi: Make snd_rawmidi_transmit() race-free
A kernel WARNING in snd_rawmidi_transmit_ack() is triggered by syzkaller fuzzer: WARNING: CPU: 1 PID: 20739 at sound/core/rawmidi.c:1136 Call Trace: [< inline >] __dump_stack lib/dump_stack.c:15 [<ffffffff82999e2d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50 [<ffffffff81352089>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482 [<ffffffff813522b9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515 [<ffffffff84f80bd5>] snd_rawmidi_transmit_ack+0x275/0x400 sound/core/rawmidi.c:1136 [<ffffffff84fdb3c1>] snd_virmidi_output_trigger+0x4b1/0x5a0 sound/core/seq/seq_virmidi.c:163 [< inline >] snd_rawmidi_output_trigger sound/core/rawmidi.c:150 [<ffffffff84f87ed9>] snd_rawmidi_kernel_write1+0x549/0x780 sound/core/rawmidi.c:1223 [<ffffffff84f89fd3>] snd_rawmidi_write+0x543/0xb30 sound/core/rawmidi.c:1273 [<ffffffff817b0323>] __vfs_write+0x113/0x480 fs/read_write.c:528 [<ffffffff817b1db7>] vfs_write+0x167/0x4a0 fs/read_write.c:577 [< inline >] SYSC_write fs/read_write.c:624 [<ffffffff817b50a1>] SyS_write+0x111/0x220 fs/read_write.c:616 [<ffffffff86336c36>] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185
Also a similar warning is found but in another path: Call Trace: [< inline >] __dump_stack lib/dump_stack.c:15 [<ffffffff82be2c0d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50 [<ffffffff81355139>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482 [<ffffffff81355369>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515 [<ffffffff8527e69a>] rawmidi_transmit_ack+0x24a/0x3b0 sound/core/rawmidi.c:1133 [<ffffffff8527e851>] snd_rawmidi_transmit_ack+0x51/0x80 sound/core/rawmidi.c:1163 [<ffffffff852d9046>] snd_virmidi_output_trigger+0x2b6/0x570 sound/core/seq/seq_virmidi.c:185 [< inline >] snd_rawmidi_output_trigger sound/core/rawmidi.c:150 [<ffffffff85285a0b>] snd_rawmidi_kernel_write1+0x4bb/0x760 sound/core/rawmidi.c:1252 [<ffffffff85287b73>] snd_rawmidi_write+0x543/0xb30 sound/core/rawmidi.c:1302 [<ffffffff817ba5f3>] __vfs_write+0x113/0x480 fs/read_write.c:528 [<ffffffff817bc087>] vfs_write+0x167/0x4a0 fs/read_write.c:577 [< inline >] SYSC_write fs/read_write.c:624 [<ffffffff817bf371>] SyS_write+0x111/0x220 fs/read_write.c:616 [<ffffffff86660276>] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185
In the former case, the reason is that virmidi has an open code calling snd_rawmidi_transmit_ack() with the value calculated outside the spinlock. We may use snd_rawmidi_transmit() in a loop just for consuming the input data, but even there, there is a race between snd_rawmidi_transmit_peek() and snd_rawmidi_tranmit_ack().
Similarly in the latter case, it calls snd_rawmidi_transmit_peek() and snd_rawmidi_tranmit_ack() separately without protection, so they are racy as well.
The patch tries to address these issues by the following ways: - Introduce the unlocked versions of snd_rawmidi_transmit_peek() and snd_rawmidi_transmit_ack() to be called inside the explicit lock. - Rewrite snd_rawmidi_transmit() to be race-free (the former case). - Make the split calls (the latter case) protected in the rawmidi spin lock.
BugLink: http://lkml.kernel.org/r/CACT4Y+YPq1+cYLkadwjWa5XjzF1_Vki1eHnVn-Lm0hzhSpu5PA... BugLink: http://lkml.kernel.org/r/CACT4Y+acG4iyphdOZx47Nyq_VHGbpJQK-6xNpiqUjaZYqsXOGw... Reported-by: Dmitry Vyukov dvyukov@google.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- include/sound/rawmidi.h | 4 ++ sound/core/rawmidi.c | 98 ++++++++++++++++++++++++++++++++------------ sound/core/seq/seq_virmidi.c | 17 +++++--- 3 files changed, 88 insertions(+), 31 deletions(-)
diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h index fdabbb4ddba9..f730b91e472f 100644 --- a/include/sound/rawmidi.h +++ b/include/sound/rawmidi.h @@ -167,6 +167,10 @@ int snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, int snd_rawmidi_transmit_ack(struct snd_rawmidi_substream *substream, int count); int snd_rawmidi_transmit(struct snd_rawmidi_substream *substream, unsigned char *buffer, int count); +int __snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, + unsigned char *buffer, int count); +int __snd_rawmidi_transmit_ack(struct snd_rawmidi_substream *substream, + int count);
/* main midi functions */
diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c index f75d1656272c..26ca02248885 100644 --- a/sound/core/rawmidi.c +++ b/sound/core/rawmidi.c @@ -1055,23 +1055,16 @@ int snd_rawmidi_transmit_empty(struct snd_rawmidi_substream *substream) EXPORT_SYMBOL(snd_rawmidi_transmit_empty);
/** - * snd_rawmidi_transmit_peek - copy data from the internal buffer + * __snd_rawmidi_transmit_peek - copy data from the internal buffer * @substream: the rawmidi substream * @buffer: the buffer pointer * @count: data size to transfer * - * Copies data from the internal output buffer to the given buffer. - * - * Call this in the interrupt handler when the midi output is ready, - * and call snd_rawmidi_transmit_ack() after the transmission is - * finished. - * - * Return: The size of copied data, or a negative error code on failure. + * This is a variant of snd_rawmidi_transmit_peek() without spinlock. */ -int snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, +int __snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, unsigned char *buffer, int count) { - unsigned long flags; int result, count1; struct snd_rawmidi_runtime *runtime = substream->runtime;
@@ -1081,7 +1074,6 @@ int snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, return -EINVAL; } result = 0; - spin_lock_irqsave(&runtime->lock, flags); if (runtime->avail >= runtime->buffer_size) { /* warning: lowlevel layer MUST trigger down the hardware */ goto __skip; @@ -1106,25 +1098,47 @@ int snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, } } __skip: + return result; +} +EXPORT_SYMBOL(__snd_rawmidi_transmit_peek); + +/** + * snd_rawmidi_transmit_peek - copy data from the internal buffer + * @substream: the rawmidi substream + * @buffer: the buffer pointer + * @count: data size to transfer + * + * Copies data from the internal output buffer to the given buffer. + * + * Call this in the interrupt handler when the midi output is ready, + * and call snd_rawmidi_transmit_ack() after the transmission is + * finished. + * + * Return: The size of copied data, or a negative error code on failure. + */ +int snd_rawmidi_transmit_peek(struct snd_rawmidi_substream *substream, + unsigned char *buffer, int count) +{ + struct snd_rawmidi_runtime *runtime = substream->runtime; + int result; + unsigned long flags; + + spin_lock_irqsave(&runtime->lock, flags); + result = __snd_rawmidi_transmit_peek(substream, buffer, count); spin_unlock_irqrestore(&runtime->lock, flags); return result; } EXPORT_SYMBOL(snd_rawmidi_transmit_peek);
/** - * snd_rawmidi_transmit_ack - acknowledge the transmission + * __snd_rawmidi_transmit_ack - acknowledge the transmission * @substream: the rawmidi substream * @count: the transferred count * - * Advances the hardware pointer for the internal output buffer with - * the given size and updates the condition. - * Call after the transmission is finished. - * - * Return: The advanced size if successful, or a negative error code on failure. + * This is a variant of __snd_rawmidi_transmit_ack() without spinlock. */ -int snd_rawmidi_transmit_ack(struct snd_rawmidi_substream *substream, int count) +int __snd_rawmidi_transmit_ack(struct snd_rawmidi_substream *substream, int count) { - unsigned long flags; struct snd_rawmidi_runtime *runtime = substream->runtime;
if (runtime->buffer == NULL) { @@ -1132,7 +1146,6 @@ int snd_rawmidi_transmit_ack(struct snd_rawmidi_substream *substream, int count) "snd_rawmidi_transmit_ack: output is not active!!!\n"); return -EINVAL; } - spin_lock_irqsave(&runtime->lock, flags); snd_BUG_ON(runtime->avail + count > runtime->buffer_size); runtime->hw_ptr += count; runtime->hw_ptr %= runtime->buffer_size; @@ -1142,9 +1155,32 @@ int snd_rawmidi_transmit_ack(struct snd_rawmidi_substream *substream, int count) if (runtime->drain || snd_rawmidi_ready(substream)) wake_up(&runtime->sleep); } - spin_unlock_irqrestore(&runtime->lock, flags); return count; } +EXPORT_SYMBOL(__snd_rawmidi_transmit_ack); + +/** + * snd_rawmidi_transmit_ack - acknowledge the transmission + * @substream: the rawmidi substream + * @count: the transferred count + * + * Advances the hardware pointer for the internal output buffer with + * the given size and updates the condition. + * Call after the transmission is finished. + * + * Return: The advanced size if successful, or a negative error code on failure. + */ +int snd_rawmidi_transmit_ack(struct snd_rawmidi_substream *substream, int count) +{ + struct snd_rawmidi_runtime *runtime = substream->runtime; + int result; + unsigned long flags; + + spin_lock_irqsave(&runtime->lock, flags); + result = __snd_rawmidi_transmit_ack(substream, count); + spin_unlock_irqrestore(&runtime->lock, flags); + return result; +} EXPORT_SYMBOL(snd_rawmidi_transmit_ack);
/** @@ -1160,12 +1196,22 @@ EXPORT_SYMBOL(snd_rawmidi_transmit_ack); int snd_rawmidi_transmit(struct snd_rawmidi_substream *substream, unsigned char *buffer, int count) { + struct snd_rawmidi_runtime *runtime = substream->runtime; + int result; + unsigned long flags; + + spin_lock_irqsave(&runtime->lock, flags); if (!substream->opened) - return -EBADFD; - count = snd_rawmidi_transmit_peek(substream, buffer, count); - if (count < 0) - return count; - return snd_rawmidi_transmit_ack(substream, count); + result = -EBADFD; + else { + count = __snd_rawmidi_transmit_peek(substream, buffer, count); + if (count <= 0) + result = count; + else + result = __snd_rawmidi_transmit_ack(substream, count); + } + spin_unlock_irqrestore(&runtime->lock, flags); + return result; } EXPORT_SYMBOL(snd_rawmidi_transmit);
diff --git a/sound/core/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c index f71aedfb408c..c82ed3e70506 100644 --- a/sound/core/seq/seq_virmidi.c +++ b/sound/core/seq/seq_virmidi.c @@ -155,21 +155,26 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream, struct snd_virmidi *vmidi = substream->runtime->private_data; int count, res; unsigned char buf[32], *pbuf; + unsigned long flags;
if (up) { vmidi->trigger = 1; if (vmidi->seq_mode == SNDRV_VIRMIDI_SEQ_DISPATCH && !(vmidi->rdev->flags & SNDRV_VIRMIDI_SUBSCRIBE)) { - snd_rawmidi_transmit_ack(substream, substream->runtime->buffer_size - substream->runtime->avail); - return; /* ignored */ + while (snd_rawmidi_transmit(substream, buf, + sizeof(buf)) > 0) { + /* ignored */ + } + return; } if (vmidi->event.type != SNDRV_SEQ_EVENT_NONE) { if (snd_seq_kernel_client_dispatch(vmidi->client, &vmidi->event, in_atomic(), 0) < 0) return; vmidi->event.type = SNDRV_SEQ_EVENT_NONE; } + spin_lock_irqsave(&substream->runtime->lock, flags); while (1) { - count = snd_rawmidi_transmit_peek(substream, buf, sizeof(buf)); + count = __snd_rawmidi_transmit_peek(substream, buf, sizeof(buf)); if (count <= 0) break; pbuf = buf; @@ -179,16 +184,18 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream, snd_midi_event_reset_encode(vmidi->parser); continue; } - snd_rawmidi_transmit_ack(substream, res); + __snd_rawmidi_transmit_ack(substream, res); pbuf += res; count -= res; if (vmidi->event.type != SNDRV_SEQ_EVENT_NONE) { if (snd_seq_kernel_client_dispatch(vmidi->client, &vmidi->event, in_atomic(), 0) < 0) - return; + goto out; vmidi->event.type = SNDRV_SEQ_EVENT_NONE; } } } + out: + spin_unlock_irqrestore(&substream->runtime->lock, flags); } else { vmidi->trigger = 0; }