On Wed, 03 Feb 2016 17:24:56 +0100, Dmitry Vyukov wrote: > > Hello, > > The following program triggers use-after-free in snd_timer_start1: > > // autogenerated by syzkaller (http://github.com/google/syzkaller) > #include <pthread.h> > #include <stdint.h> > #include <string.h> > #include <sys/syscall.h> > #include <unistd.h> > > int main() > { > syscall(SYS_mmap, 0x20000000ul, 0x664000ul, 0x3ul, 0x32ul, > 0xfffffffffffffffful, 0x0ul); > int fd = syscall(SYS_open, "/dev/snd/timer", 0x40000ul, 0, 0, 0); > *(uint32_t*)0x20653000 = (uint32_t)0x1; > *(uint32_t*)0x20653004 = (uint32_t)0xfffffffffffffffe; > *(uint32_t*)0x20653008 = (uint32_t)0x8; > *(uint32_t*)0x2065300c = (uint32_t)0x0; > *(uint32_t*)0x20653010 = (uint32_t)0x0; > *(uint8_t*)0x20653014 = (uint8_t)0x0; > *(uint8_t*)0x20653015 = (uint8_t)0x0; > *(uint8_t*)0x20653016 = (uint8_t)0x0; > *(uint8_t*)0x20653017 = (uint8_t)0x0; > *(uint8_t*)0x20653018 = (uint8_t)0x0; > *(uint8_t*)0x20653019 = (uint8_t)0x0; > *(uint8_t*)0x2065301a = (uint8_t)0x0; > *(uint8_t*)0x2065301b = (uint8_t)0x0; > *(uint8_t*)0x2065301c = (uint8_t)0x0; > *(uint8_t*)0x2065301d = (uint8_t)0x0; > *(uint8_t*)0x2065301e = (uint8_t)0x0; > *(uint8_t*)0x2065301f = (uint8_t)0x0; > *(uint8_t*)0x20653020 = (uint8_t)0x0; > *(uint8_t*)0x20653021 = (uint8_t)0x0; > *(uint8_t*)0x20653022 = (uint8_t)0x0; > *(uint8_t*)0x20653023 = (uint8_t)0x0; > *(uint8_t*)0x20653024 = (uint8_t)0x0; > *(uint8_t*)0x20653025 = (uint8_t)0x0; > *(uint8_t*)0x20653026 = (uint8_t)0x0; > *(uint8_t*)0x20653027 = (uint8_t)0x0; > *(uint8_t*)0x20653028 = (uint8_t)0x0; > *(uint8_t*)0x20653029 = (uint8_t)0x0; > *(uint8_t*)0x2065302a = (uint8_t)0x0; > *(uint8_t*)0x2065302b = (uint8_t)0x0; > *(uint8_t*)0x2065302c = (uint8_t)0x0; > *(uint8_t*)0x2065302d = (uint8_t)0x0; > *(uint8_t*)0x2065302e = (uint8_t)0x0; > *(uint8_t*)0x2065302f = (uint8_t)0x0; > *(uint8_t*)0x20653030 = (uint8_t)0x0; > *(uint8_t*)0x20653031 = (uint8_t)0x0; > *(uint8_t*)0x20653032 = (uint8_t)0x0; > *(uint8_t*)0x20653033 = (uint8_t)0x0; > syscall(SYS_ioctl, fd, 0x40345410ul, 0x20653000ul, 0, 0, 0); > syscall(SYS_ioctl, fd, 0x54a0ul, 0, 0, 0, 0); > return 0; > } > > ================================================================== > BUG: KASAN: use-after-free in __list_add+0x233/0x22016/02/03 13:44:32 > executing program 0: > Read of size 8 by task syz-executor/27661 > > INFO: Allocated in snd_timer_instance_new+0x52/0x3a0 age=7 cpu=0 pid=27660 > [< inline >] slab_alloc_node mm/slub.c:2562 > [< inline >] slab_alloc mm/slub.c:2604 > [< none >] kmem_cache_alloc_trace+0x25c/0x300 mm/slub.c:2621 > [< inline >] kmalloc include/linux/slab.h:463 > [< inline >] kzalloc include/linux/slab.h:607 > [< none >] snd_timer_instance_new+0x52/0x3a0 sound/core/timer.c:106 > [< none >] snd_timer_open+0x522/0xd20 sound/core/timer.c:289 > [< inline >] snd_timer_user_tselect sound/core/timer.c:1598 > [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1874 > [< none >] snd_timer_user_ioctl+0x8db/0x25f0 sound/core/timer.c:1904 > [< inline >] vfs_ioctl fs/ioctl.c:43 > [< none >] do_vfs_ioctl+0x18c/0xfb0 fs/ioctl.c:674 > [< inline >] SYSC_ioctl fs/ioctl.c:689 > [< none >] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:680 > [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a > arch/x86/entry/entry_64.S:185 > > INFO: Freed in snd_timer_close+0x3ee/0x750 age=9 cpu=3 pid=27661 > [< inline >] slab_free mm/slub.c:2835 > [< none >] kfree+0x2ac/0x2c0 mm/slub.c:3664 > [< none >] snd_timer_close+0x3ee/0x750 sound/core/timer.c:375 > [< inline >] snd_timer_user_tselect sound/core/timer.c:1588 > [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1874 > [< none >] snd_timer_user_ioctl+0x7b6/0x25f0 sound/core/timer.c:1904 > [< inline >] vfs_ioctl fs/ioctl.c:43 > [< none >] do_vfs_ioctl+0x18c/0xfb0 fs/ioctl.c:674 > [< inline >] SYSC_ioctl fs/ioctl.c:689 > [< none >] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:680 > [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a > arch/x86/entry/entry_64.S:185 > > Call Trace: > [< inline >] kasan_report mm/kasan/report.c:274 > [<ffffffff8176640e>] __asan_report_load8_noabort+0x3e/0x40 > mm/kasan/report.c:295 > [<ffffffff82c4a7e3>] __list_add+0x233/0x250 lib/list_debug.c:39 > [< inline >] list_move_tail include/linux/list.h:77 > [<ffffffff85240fdc>] snd_timer_start1+0x6c/0x2c0 sound/core/timer.c:432 > [<ffffffff85241a7b>] snd_timer_start+0x20b/0x2b0 sound/core/timer.c:499 > [< inline >] snd_timer_user_start sound/core/timer.c:1799 > [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1883 > [<ffffffff85245fb7>] snd_timer_user_ioctl+0x767/0x25f0 sound/core/timer.c:1904 > [< inline >] vfs_ioctl fs/ioctl.c:43 > [<ffffffff817fa9ec>] do_vfs_ioctl+0x18c/0xfb0 fs/ioctl.c:674 > [< inline >] SYSC_ioctl fs/ioctl.c:689 > [<ffffffff817fb89f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:680 > [<ffffffff8665ebb6>] entry_SYSCALL_64_fastpath+0x16/0x7a > arch/x86/entry/entry_64.S:185 > ================================================================== > > > Sometimes it manifests as: > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 6548 at lib/list_debug.c:42 __list_add+0x1db/0x250() > list_add corruption. prev->next should be next (ffff8800697c10e8), but > was ffff880030441fd0. (prev=ffff880030441fd0). > Modules linked in: > CPU: 1 PID: 6548 Comm: a.out Not tainted 4.5.0-rc2+ #309 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > 00000000ffffffff ffff88002fa17918 ffffffff82be2c8d ffff88002fa17988 > ffff88002fd62f80 ffffffff86acf380 ffff88002fa17958 ffffffff81355139 > ffffffff82c4a78b ffffed0005f42f2d ffffffff86acf380 000000000000002a > Call Trace: > [< inline >] __dump_stack lib/dump_stack.c:15 > [<ffffffff82be2c8d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50 > [<ffffffff81355139>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482 > [<ffffffff81355249>] warn_slowpath_fmt+0xa9/0xd0 kernel/panic.c:494 > [<ffffffff82c4a78b>] __list_add+0x1db/0x250 lib/list_debug.c:39 > [< inline >] list_move_tail include/linux/list.h:77 > [<ffffffff85240fdc>] snd_timer_start1+0x6c/0x2c0 sound/core/timer.c:432 > [<ffffffff85241a7b>] snd_timer_start+0x20b/0x2b0 sound/core/timer.c:499 > [< inline >] snd_timer_user_start sound/core/timer.c:1799 > [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1883 > [<ffffffff85245fb7>] snd_timer_user_ioctl+0x767/0x25f0 sound/core/timer.c:1904 > [< inline >] vfs_ioctl fs/ioctl.c:43 > [<ffffffff817fa9ec>] do_vfs_ioctl+0x18c/0xfb0 fs/ioctl.c:674 > [< inline >] SYSC_ioctl fs/ioctl.c:689 > [<ffffffff817fb89f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:680 > [<ffffffff8665ebb6>] entry_SYSCALL_64_fastpath+0x16/0x7a > arch/x86/entry/entry_64.S:185 > ---[ end trace 77da812dd399e78b ]--- > > On commit 34229b277480f46c1e9a19f027f30b074512e68b + recent fixes from Takashi. Thanks for the report. This is indeed an old bug, but it appears now more easily due to the recent fix to avoid double-stop. Below is the fix patch. topic/core-fixes branch was updated with this, too. Takashi -- 8< -- From: Takashi Iwai <tiwai@xxxxxxx> Subject: [PATCH] ALSA: timer: Fix leftover link at closing In ALSA timer core, the active timer instance is managed in active_list linked list. Each element is added / removed dynamically at timer start, stop and in timer interrupt. The problem is that snd_timer_interrupt() has a thinko and leaves the element in active_list when it's the last opened element. This eventually leads to list corruption or use-after-free error. This hasn't been revealed because we used to delete the list forcibly in snd_timer_stop() in the past. However, the recent fix avoids the double-stop behavior (in commit [f784beb75ce8: ALSA: timer: Fix link corruption due to double start or stop]), and this leak hits reality. This patch fixes the link management in snd_timer_interrupt(). Now it simply unlinks no matter which stream is. BugLink: http://lkml.kernel.org/r/CACT4Y+Yy2aukHP-EDp8-ziNqNNmb-NTf=jDWXMP7jB8HDa2vng@xxxxxxxxxxxxxx Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> --- sound/core/timer.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/sound/core/timer.c b/sound/core/timer.c index b419e612f987..9b513a05765a 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -744,8 +744,8 @@ void snd_timer_interrupt(struct snd_timer * timer, unsigned long ticks_left) ti->cticks = ti->ticks; } else { ti->flags &= ~SNDRV_TIMER_IFLG_RUNNING; - if (--timer->running) - list_del_init(&ti->active_list); + --timer->running; + list_del_init(&ti->active_list); } if ((timer->hw.flags & SNDRV_TIMER_HW_TASKLET) || (ti->flags & SNDRV_TIMER_IFLG_FAST)) -- 2.7.0 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
