[PATCH 3.16 049/254] ALSA: usb-audio: Fix out-of-bound error

Ben Hutchings
2018-02-28T16:05:14Z

From: Jaejoong Kim <climbbb.kim@gmail.com>

commit 251552a2b0d454badc8f486e6d79100970c744b0 upstream.

The snd_usb_copy_string_desc() retrieves the usb string corresponding to
the index number through the usb_string(). The problem is that the
usb_string() returns the length of the string (>= 0) when successful, but
it can also return a negative value about the error case or status of
usb_control_msg().

If iClockSource is '0' as shown below, usb_string() will returns -EINVAL.
This will result in '0' being inserted into buf[-22], and the following
KASAN out-of-bound error message will be output.

AudioControl Interface Descriptor:
bLength 8
bDescriptorType 36
bDescriptorSubtype 10 (CLOCK_SOURCE)
bClockID 1
bmAttributes 0x07 Internal programmable Clock (synced to SOF)
bmControls 0x07
Clock Frequency Control (read/write)
Clock Validity Control (read-only)
bAssocTerminal 0
iClockSource 0

To fix it, check usb_string()'return value and bail out.

==================================================================
BUG: KASAN: stack-out-of-bounds in parse_audio_unit+0x1327/0x1960 [snd_usb_audio]
Write of size 1 at addr ffff88007e66735a by task systemd-udevd/18376

CPU: 0 PID: 18376 Comm: systemd-udevd Not tainted 4.13.0+ #3
Hardware name: LG Electronics 15N540-RFLGL/White Tip Mountain, BIOS 15N5
Call Trace:
dump_stack+0x63/0x8d
print_address_description+0x70/0x290
? parse_audio_unit+0x1327/0x1960 [snd_usb_audio]
kasan_report+0x265/0x350
__asan_store1+0x4a/0x50
parse_audio_unit+0x1327/0x1960 [snd_usb_audio]
? save_stack+0xb5/0xd0
? save_stack_trace+0x1b/0x20
? save_stack+0x46/0xd0
? kasan_kmalloc+0xad/0xe0
? kmem_cache_alloc_trace+0xff/0x230
? snd_usb_create_mixer+0xb0/0x4b0 [snd_usb_audio]
? usb_audio_probe+0x4de/0xf40 [snd_usb_audio]
? usb_probe_interface+0x1f5/0x440
? driver_probe_device+0x3ed/0x660
? build_feature_ctl+0xb10/0xb10 [snd_usb_audio]
? save_stack_trace+0x1b/0x20
? init_object+0x69/0xa0
? snd_usb_find_csint_desc+0xa8/0xf0 [snd_usb_audio]
snd_usb_mixer_controls+0x1dc/0x370 [snd_usb_audio]
? build_audio_procunit+0x890/0x890 [snd_usb_audio]
? snd_usb_create_mixer+0xb0/0x4b0 [snd_usb_audio]
? kmem_cache_alloc_trace+0xff/0x230
? usb_ifnum_to_if+0xbd/0xf0
snd_usb_create_mixer+0x25b/0x4b0 [snd_usb_audio]
? snd_usb_create_stream+0x255/0x2c0 [snd_usb_audio]
usb_audio_probe+0x4de/0xf40 [snd_usb_audio]
? snd_usb_autosuspend.part.7+0x30/0x30 [snd_usb_audio]
? __pm_runtime_idle+0x90/0x90
? kernfs_activate+0xa6/0xc0
? usb_match_one_id_intf+0xdc/0x130
? __pm_runtime_set_status+0x2d4/0x450
usb_probe_interface+0x1f5/0x440

Signed-off-by: Jaejoong Kim <climbbb.kim@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
sound/usb/mixer.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -199,6 +199,10 @@ static int snd_usb_copy_string_desc(stru
int index, char *buf, int maxlen)
{
int len = usb_string(state->chip->dev, index, buf, maxlen - 1);
+
+ if (len < 0)
+ return 0;
+
buf[len] = 0;
return len;
}