From 838e1030d96ad548f73cfb368717242fa7743bbe Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Wed, 6 Nov 2019 17:55:47 +0100 Subject: [PATCH] [RAMEN9610-21500]ALSA: timer: Fix incorrectly assigned timer instance commit e7af6307a8a54f0b873960b32b6a644f2d0fbd97 upstream. The clean up commit 41672c0c24a6 ("ALSA: timer: Simplify error path in snd_timer_open()") unified the error handling code paths with the standard goto, but it introduced a subtle bug: the timer instance is stored in snd_timer_open() incorrectly even if it returns an error. This may eventually lead to UAF, as spotted by fuzzer. The culprit is the snd_timer_open() code checks the SNDRV_TIMER_IFLG_EXCLUSIVE flag with the common variable timeri. This variable is supposed to be the newly created instance, but we (ab-)used it for a temporary check before the actual creation of a timer instance. After that point, there is another check for the max number of instances, and it bails out if over the threshold. Before the refactoring above, it worked fine because the code returned directly from that point. After the refactoring, however, it jumps to the unified error path that stores the timeri variable in return -- even if it returns an error. Unfortunately this stored value is kept in the caller side (snd_timer_user_tselect()) in tu->timeri. This causes inconsistency later, as if the timer was successfully assigned. In this patch, we fix it by not re-using timeri variable but a temporary variable for testing the exclusive connection, so timeri remains NULL at that point. Change-Id: Ie29761330ecc8fef9e0ff56657b079d80c26989f Fixes: 41672c0c24a6 ("ALSA: timer: Simplify error path in snd_timer_open()") Reported-and-tested-by: Tristan Madani Cc: Link: https://lore.kernel.org/r/20191106165547.23518-1-tiwai@suse.de Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/timer.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/sound/core/timer.c b/sound/core/timer.c index 161ab19cb722..c60dfd52e8a6 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -298,11 +298,11 @@ int snd_timer_open(struct snd_timer_instance **ti, goto unlock; } if (!list_empty(&timer->open_list_head)) { - timeri = list_entry(timer->open_list_head.next, + struct snd_timer_instance *t = + list_entry(timer->open_list_head.next, struct snd_timer_instance, open_list); - if (timeri->flags & SNDRV_TIMER_IFLG_EXCLUSIVE) { + if (t->flags & SNDRV_TIMER_IFLG_EXCLUSIVE) { err = -EBUSY; - timeri = NULL; goto unlock; } } -- 2.20.1