Description
In the Linux kernel, the following vulnerability has been resolved: ALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes snd_timer_close_locked() marks an instance with SNDRV_TIMER_IFLG_DEAD and returns early when the flag is already set, but the flag is never cleared again. A completed close ends in remove_slave_links(), which leaves timeri->timer NULL, so a second close is already harmless through the timer == NULL path; the early return can only be reached by an instance that was opened again in between. For such an instance the close unlinks nothing, so snd_timer_instance_free() frees an object that is still on timer->open_list_head, still on snd_timer_master_list if it was opened with a slave key, still owns any adopted slaves, and still holds its timer and module references. snd_seq_timer_open() reopens an instance exactly like that: it retries its fallback open on the same object after a failure that has already run snd_timer_close_locked() internally. An unprivileged user with access to /dev/snd/timer and /dev/snd/seq can force that failure, since snd_timer_check_master() returns -EBUSY when a pending slave matches the new master's (slave_class, slave_id) key and the target timer has reached max_instances, and SNDRV_TIMER_IOCTL_SELECT with dev_class = SNDRV_TIMER_CLASS_SLAVE keeps the caller-supplied dev_sclass, so a sequencer queue's key can be forged. The freed instance is afterwards dereferenced by any further snd_timer_open() on that timer, by snd_timer_check_slave(), and by /proc/asound/timers, which faults on the stale ti->owner pointer. The flag only has to be visible while the close is in progress, which is all its other users need. Clear it in remove_slave_links(), under the same timer->lock that sets it, once the instance is off every list.
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
Linux Linux
Default version status: unaffected
586b219a22b1032b28b8bd356b963276c5e5bf53 to < bb016091010ec401a06e6bdace0cd944ee03d371affectedf46093dd22969037beb1fce2e043f3236be41c92 to < a26a2e52736f9e39843ca66a2e1ce6bf1adbcd1eaffectedda3039e91d1f835874ed6e9a33ea19ee80c2cb92 to < 0c561fab50991df10b1e4daca25886c34a2a9c07affectedda3039e91d1f835874ed6e9a33ea19ee80c2cb92 to < c2744d5f3aea474513fd2298daecb94a952ce441affected60e73ab87b84bbd6bd7ddd1d16019a3a3705ab8faffected6.12.94 to < 6.12.103affected6.18.36 to < 6.18.44affected7.0.13 to < 7.1affected
Linux Linux
Default version status: affected
7.1affected0 to < 7.1unaffected6.12.103 to ≤ 6.12.*unaffected6.18.44 to ≤ 6.18.*unaffected7.1.8 to ≤ 7.1.*unaffected7.2 to ≤ *unaffected