Hi! On Mon, Aug 02 2021 at 01:49, syzbot wrote: > syzbot found the following issue on: > > HEAD commit: 4010a528219e Merge tag 'fixes_for_v5.14-rc4' of git://git... > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=13611f5c300000 > kernel config: https://syzkaller.appspot.com/x/.config?x=1dee114394f7d2c2 > dashboard link: https://syzkaller.appspot.com/bug?extid=66e110c312ed4ae684a8 > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1 > > Unfortunately, I don't have any reproducer for this issue yet. > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+66e110c312ed4ae684a8@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KASAN: use-after-free in timerfd_clock_was_set+0x2b8/0x2e0 > fs/timerfd.c:104 103 rcu_read_lock(); 104 list_for_each_entry_rcu(ctx, &cancel_list, clist) { > timerfd_clock_was_set+0x2b8/0x2e0 fs/timerfd.c:104 > timekeeping_inject_offset+0x4af/0x620 kernel/time/timekeeping.c:1375 > do_adjtimex+0x28f/0xa30 kernel/time/timekeeping.c:2406 > do_clock_adjtime kernel/time/posix-timers.c:1109 [inline] > __do_sys_clock_adjtime+0x163/0x270 kernel/time/posix-timers.c:1121 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 ... > Allocated by task 1: > kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 > kasan_set_track mm/kasan/common.c:46 [inline] > set_alloc_info mm/kasan/common.c:434 [inline] > ____kasan_kmalloc mm/kasan/common.c:513 [inline] > ____kasan_kmalloc mm/kasan/common.c:472 [inline] > __kasan_kmalloc+0x98/0xc0 mm/kasan/common.c:522 > kasan_kmalloc include/linux/kasan.h:264 [inline] > kmem_cache_alloc_trace+0x1e4/0x480 mm/slab.c:3575 > kmalloc include/linux/slab.h:591 [inline] > kzalloc include/linux/slab.h:721 [inline] > __do_sys_timerfd_create+0x265/0x370 fs/timerfd.c:412 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x44/0xae ... > Freed by task 3306: > kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 > kasan_set_track+0x1c/0x30 mm/kasan/common.c:46 > kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:360 > ____kasan_slab_free mm/kasan/common.c:366 [inline] > ____kasan_slab_free mm/kasan/common.c:328 [inline] > __kasan_slab_free+0xcd/0x100 mm/kasan/common.c:374 > kasan_slab_free include/linux/kasan.h:230 [inline] > __cache_free mm/slab.c:3445 [inline] > kfree+0x106/0x2c0 mm/slab.c:3803 > kvfree+0x42/0x50 mm/util.c:616 > kfree_rcu_work+0x5b7/0x870 kernel/rcu/tree.c:3359 > process_one_work+0x98d/0x1630 kernel/workqueue.c:2276 > worker_thread+0x658/0x11f0 kernel/workqueue.c:2422 > kthread+0x3e5/0x4d0 kernel/kthread.c:319 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 So the free of the timerfd context happens while the context is still linked in the cancel list, which does not make sense because > Last potentially related work creation: > kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 > kasan_record_aux_stack+0xa4/0xd0 mm/kasan/generic.c:348 > kvfree_call_rcu+0x74/0x990 kernel/rcu/tree.c:3594 > timerfd_release+0x105/0x290 fs/timerfd.c:229 timerfd_release() invokes timerfd_remove_cancel(context) before invoking kfree_rcu(). > __fput+0x288/0x920 fs/file_table.c:280 > task_work_run+0xdd/0x1a0 kernel/task_work.c:164 > tracehook_notify_resume include/linux/tracehook.h:189 [inline] > exit_to_user_mode_loop kernel/entry/common.c:175 [inline] > exit_to_user_mode_prepare+0x27e/0x290 kernel/entry/common.c:209 > __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline] > syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:302 > do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86 > entry_SYSCALL_64_after_hwframe+0x44/0xae The only reason why timerfd_remove_cancel() would not remove it from the list is when context->might_cancel is false. But that would mean it's a memory corruption of some sort which went undetected. I can't spot anything in the timerfd code itself which would cause that. Confused. Thanks, tglx
