[PATCH] ALSA: control: Fix an out-of-bounds bug in get_ctl_id_hash()

[Zheyu Ma]

Since the user can control the arguments provided to the kernel by the
ioctl() system call, an out-of-bounds bug occurs when the 'id->name'
provided by the user does not end with '\0'.

The following log can reveal it:

[    10.002313] BUG: KASAN: stack-out-of-bounds in snd_ctl_find_id+0x36c/0x3a0
[    10.002895] Read of size 1 at addr ffff888109f5fe28 by task snd/439
[    10.004934] Call Trace:
[    10.007140]  snd_ctl_find_id+0x36c/0x3a0
[    10.007489]  snd_ctl_ioctl+0x6cf/0x10e0

Fix this by checking the bound of 'id->name' in the loop.

Fixes: c27e1efb61c5 ("ALSA: control: Use xarray for faster lookups")
Signed-off-by: Zheyu Ma <zheyuma97 at gmail.com>
---
 sound/core/control.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sound/core/control.c b/sound/core/control.c
index f3e893715369..e8fc4c511e5f 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -385,14 +385,14 @@ static bool elem_id_matches(const struct snd_kcontrol *kctl,
 #define MULTIPLIER	37
 static unsigned long get_ctl_id_hash(const struct snd_ctl_elem_id *id)
 {
+	int i;
 	unsigned long h;
-	const unsigned char *p;
 
 	h = id->iface;
 	h = MULTIPLIER * h + id->device;
 	h = MULTIPLIER * h + id->subdevice;
-	for (p = id->name; *p; p++)
-		h = MULTIPLIER * h + *p;
+	for (i = 0; id->name[i] && i < SNDRV_CTL_ELEM_ID_NAME_MAXLEN; i++)
+		h = MULTIPLIER * h + id->name[i];
 	h = MULTIPLIER * h + id->index;
 	h &= LONG_MAX;
 	return h;
-- 
2.25.1