[PATCH] soundwire: intel: fix possible crash when no device is detected (was Re: Crash in acpi_ns_validate_handle triggered by soundwire on Linux 5.10)

[Marcin Ślusarz]

Well, this is embarrassing. There's no compiler bug, just me being
confused, because I looked at handle instead of *handle.
The stack protector thing was of course a red herring - it
changed what is on the stack and where...

If the patch below will be corrupted by the Gmail interface, I also
pushed it here:
https://github.com/marcinslusarz/linux/tree/soundwire_fix

----
From: =?UTF-8?q?Marcin=20=C5=9Alusarz?= <marcin.slusarz at intel.com>
Subject: [PATCH] soundwire: intel: fix possible crash when no device is
 detected

acpi_walk_namespace can return success without executing our
callback which initializes info->handle.
If the random value in this structure is a valid address (which
is on the stack, so it's quite possible), then nothing bad will
happen, because:
sdw_intel_scan_controller
 -> acpi_bus_get_device
 -> acpi_get_device_data
 -> acpi_get_data_full
 -> acpi_ns_validate_handle
will reject this handle.

However, if the value from the stack doesn't point to a valid
address, we get this:

BUG: kernel NULL pointer dereference, address: 0000000000000050
PGD 0 P4D 0
Oops: 0000 [#1] SMP NOPTI
CPU: 6 PID: 472 Comm: systemd-udevd Tainted: G        W
5.10.0-1-amd64 #1 Debian 5.10.4-1
Hardware name: HP HP Pavilion Laptop 15-cs3xxx/86E2, BIOS F.05 01/01/2020
RIP: 0010:acpi_ns_validate_handle+0x1a/0x23
Code: 00 48 83 c4 10 5b 5d 41 5c 41 5d 41 5e 41 5f c3 0f 1f 44 00 00
48 8d 57 ff 48 89 f8 48 83 fa fd 76 08 48 8b 05 0c b8 67 01 c3 <80> 7f
08 0f 74 02 31 c0 c3 0f 1f 44 00 00 48 8b 3d f6 b7 67 01 e8
RSP: 0000:ffffc388807c7b20 EFLAGS: 00010213
RAX: 0000000000000048 RBX: ffffc388807c7b70 RCX: 0000000000000000
RDX: 0000000000000047 RSI: 0000000000000246 RDI: 0000000000000048
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffffc0f5f4d1 R11: ffffffff8f0cb268 R12: 0000000000001001
R13: ffffffff8e33b160 R14: 0000000000000048 R15: 0000000000000000
FS:  00007f24548288c0(0000) GS:ffff9f781fb80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000050 CR3: 0000000106158004 CR4: 0000000000770ee0
PKRU: 55555554
Call Trace:
 acpi_get_data_full+0x4d/0x92
 acpi_bus_get_device+0x1f/0x40
 sdw_intel_acpi_scan+0x59/0x230 [soundwire_intel]
 ? strstr+0x22/0x60
 ? dmi_matches+0x76/0xe0
 snd_intel_dsp_driver_probe.cold+0xaf/0x163 [snd_intel_dspcfg]
 azx_probe+0x7a/0x970 [snd_hda_intel]
 local_pci_probe+0x42/0x80
 ? _cond_resched+0x16/0x40
 pci_device_probe+0xfd/0x1b0
 really_probe+0x205/0x460
 driver_probe_device+0xe1/0x150
 device_driver_attach+0xa1/0xb0
 __driver_attach+0x8a/0x150
 ? device_driver_attach+0xb0/0xb0
 ? device_driver_attach+0xb0/0xb0
 bus_for_each_dev+0x78/0xc0
 bus_add_driver+0x12b/0x1e0
 driver_register+0x8b/0xe0
 ? 0xffffffffc0f65000
 do_one_initcall+0x44/0x1d0
 ? do_init_module+0x23/0x250
 ? kmem_cache_alloc_trace+0xf5/0x200
 do_init_module+0x5c/0x250
 __do_sys_finit_module+0xb1/0x110
 do_syscall_64+0x33/0x80
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

CC: stable at vger.kernel.org
Signed-off-by: Marcin Ślusarz <marcin.slusarz at intel.com>
---
 drivers/soundwire/intel_init.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/intel_init.c b/drivers/soundwire/intel_init.c
index cabdadb09a1b..bc8520eb385e 100644
--- a/drivers/soundwire/intel_init.c
+++ b/drivers/soundwire/intel_init.c
@@ -405,11 +405,12 @@ int sdw_intel_acpi_scan(acpi_handle *parent_handle,
 {
     acpi_status status;

+    info->handle = NULL;
     status = acpi_walk_namespace(ACPI_TYPE_DEVICE,
                      parent_handle, 1,
                      sdw_intel_acpi_cb,
                      NULL, info, NULL);
-    if (ACPI_FAILURE(status))
+    if (ACPI_FAILURE(status) || info->handle == NULL)
         return -ENODEV;

     return sdw_intel_scan_controller(info);
-- 
2.29.2