sound: Prevent buffer overflow in OSS load_mixer_volumes

The load_mixer_volumes() function, which can be triggered by
unprivileged users via the SOUND_MIXER_SETLEVELS ioctl, is vulnerable to
a buffer overflow.  Because the provided "name" argument isn't
guaranteed to be NULL terminated at the expected 32 bytes, it's possible
to overflow past the end of the last element in the mixer_vols array.
Further exploitation can result in an arbitrary kernel write (via
subsequent calls to load_mixer_volumes()) leading to privilege
escalation, or arbitrary kernel reads via get_mixer_levels().  In
addition, the strcmp() may leak bytes beyond the mixer_vols array.

Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/oss/soundcard.c b/sound/oss/soundcard.c
index 46c0d03dbecced68ca318dbbe20df52d1da4ab0b..fcb14a09982262d473842aeb55f365b031ebeb70 100644 (file)
--- a/sound/oss/soundcard.c
+++ b/sound/oss/soundcard.c
@@ -87,7 +87,7 @@ int *load_mixer_volumes(char *name, int *levels, int present)
        int             i, n;
 
        for (i = 0; i < num_mixer_volumes; i++) {
-               if (strcmp(name, mixer_vols[i].name) == 0) {
+               if (strncmp(name, mixer_vols[i].name, 32) == 0) {
                        if (present)
                                mixer_vols[i].num = i;
                        return mixer_vols[i].levels;
@@ -99,7 +99,7 @@ int *load_mixer_volumes(char *name, int *levels, int present)
        }
        n = num_mixer_volumes++;
 
-       strcpy(mixer_vols[n].name, name);
+       strncpy(mixer_vols[n].name, name, 32);
 
        if (present)
                mixer_vols[n].num = n;