On Tue, Nov 27, 2018 at 9:06 AM syzbot <syzbot+695726bc473f9c36a4b6@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > syzbot has found a reproducer for the following crash on: > > HEAD commit: 6f8b52ba442c Merge tag 'hwmon-for-v4.20-rc5' of git://git... > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=120f3905400000 > kernel config: https://syzkaller.appspot.com/x/.config?x=c94f9f0c0363db4b > dashboard link: https://syzkaller.appspot.com/bug?extid=695726bc473f9c36a4b6 > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10cad225400000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13813093400000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+695726bc473f9c36a4b6@xxxxxxxxxxxxxxxxxxxxxxxxx > > overlayfs: filesystem on './file0' not supported as upperdir > > ====================================================== > WARNING: possible circular locking dependency detected > 4.20.0-rc4+ #351 Not tainted > ------------------------------------------------------ > syz-executor338/5996 is trying to acquire lock: > 00000000b59bb66d (&ovl_i_mutex_key[depth]){+.+.}, at: inode_lock > include/linux/fs.h:757 [inline] > 00000000b59bb66d (&ovl_i_mutex_key[depth]){+.+.}, at: > ovl_write_iter+0x151/0xd10 fs/overlayfs/file.c:231 > > but task is already holding lock: > 00000000e0274330 (&pipe->mutex/1){+.+.}, at: pipe_lock_nested fs/pipe.c:62 > [inline] > 00000000e0274330 (&pipe->mutex/1){+.+.}, at: pipe_lock+0x6e/0x80 > fs/pipe.c:70 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #2 (&pipe->mutex/1){+.+.}: > __mutex_lock_common kernel/locking/mutex.c:925 [inline] > __mutex_lock+0x166/0x16f0 kernel/locking/mutex.c:1072 > mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087 > pipe_lock_nested fs/pipe.c:62 [inline] > pipe_lock+0x6e/0x80 fs/pipe.c:70 > iter_file_splice_write+0x27d/0x1050 fs/splice.c:700 > do_splice_from fs/splice.c:851 [inline] > do_splice+0x64a/0x1430 fs/splice.c:1147 > __do_sys_splice fs/splice.c:1414 [inline] > __se_sys_splice fs/splice.c:1394 [inline] > __x64_sys_splice+0x2c1/0x330 fs/splice.c:1394 > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > -> #1 (sb_writers#3){.+.+}: > percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 > [inline] > percpu_down_read include/linux/percpu-rwsem.h:59 [inline] > __sb_start_write+0x214/0x370 fs/super.c:1387 > sb_start_write include/linux/fs.h:1597 [inline] > mnt_want_write+0x3f/0xc0 fs/namespace.c:360 > ovl_want_write+0x76/0xa0 fs/overlayfs/util.c:24 > ovl_setattr+0x10b/0xaf0 fs/overlayfs/inode.c:30 > notify_change+0xbde/0x1110 fs/attr.c:334 > do_truncate+0x1bd/0x2d0 fs/open.c:63 > handle_truncate fs/namei.c:3008 [inline] > do_last fs/namei.c:3424 [inline] > path_openat+0x375f/0x5150 fs/namei.c:3534 > do_filp_open+0x255/0x380 fs/namei.c:3564 > do_sys_open+0x568/0x700 fs/open.c:1063 > __do_sys_openat fs/open.c:1090 [inline] > __se_sys_openat fs/open.c:1084 [inline] > __x64_sys_openat+0x9d/0x100 fs/open.c:1084 > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > -> #0 (&ovl_i_mutex_key[depth]){+.+.}: > lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844 > down_write+0x8a/0x130 kernel/locking/rwsem.c:70 > inode_lock include/linux/fs.h:757 [inline] > ovl_write_iter+0x151/0xd10 fs/overlayfs/file.c:231 > call_write_iter include/linux/fs.h:1857 [inline] > new_sync_write fs/read_write.c:474 [inline] > __vfs_write+0x6b8/0x9f0 fs/read_write.c:487 > __kernel_write+0x10c/0x370 fs/read_write.c:506 > write_pipe_buf+0x180/0x240 fs/splice.c:797 > splice_from_pipe_feed fs/splice.c:503 [inline] > __splice_from_pipe+0x38b/0x7c0 fs/splice.c:627 > splice_from_pipe+0x1ec/0x340 fs/splice.c:662 > default_file_splice_write+0x3c/0x90 fs/splice.c:809 > do_splice_from fs/splice.c:851 [inline] > do_splice+0x64a/0x1430 fs/splice.c:1147 > __do_sys_splice fs/splice.c:1414 [inline] > __se_sys_splice fs/splice.c:1394 [inline] > __x64_sys_splice+0x2c1/0x330 fs/splice.c:1394 > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > other info that might help us debug this: > > Chain exists of: > &ovl_i_mutex_key[depth] --> sb_writers#3 --> &pipe->mutex/1 > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&pipe->mutex/1); > lock(sb_writers#3); > lock(&pipe->mutex/1); > lock(&ovl_i_mutex_key[depth]); > > *** DEADLOCK *** > > 2 locks held by syz-executor338/5996: > #0: 00000000024e7b73 (sb_writers#8){.+.+}, at: file_start_write > include/linux/fs.h:2810 [inline] > #0: 00000000024e7b73 (sb_writers#8){.+.+}, at: do_splice+0xd2e/0x1430 > fs/splice.c:1146 > #1: 00000000e0274330 (&pipe->mutex/1){+.+.}, at: pipe_lock_nested > fs/pipe.c:62 [inline] > #1: 00000000e0274330 (&pipe->mutex/1){+.+.}, at: pipe_lock+0x6e/0x80 > fs/pipe.c:70 > > stack backtrace: > CPU: 0 PID: 5996 Comm: syz-executor338 Not tainted 4.20.0-rc4+ #351 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x244/0x39d lib/dump_stack.c:113 > print_circular_bug.isra.35.cold.54+0x1bd/0x27d > kernel/locking/lockdep.c:1221 > check_prev_add kernel/locking/lockdep.c:1863 [inline] > check_prevs_add kernel/locking/lockdep.c:1976 [inline] > validate_chain kernel/locking/lockdep.c:2347 [inline] > __lock_acquire+0x3399/0x4c20 kernel/locking/lockdep.c:3341 > lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844 > down_write+0x8a/0x130 kernel/locking/rwsem.c:70 > inode_lock include/linux/fs.h:757 [inline] > ovl_write_iter+0x151/0xd10 fs/overlayfs/file.c:231 > call_write_iter include/linux/fs.h:1857 [inline] > new_sync_write fs/read_write.c:474 [inline] > __vfs_write+0x6b8/0x9f0 fs/read_write.c:487 > __kernel_write+0x10c/0x370 fs/read_write.c:506 > write_pipe_buf+0x180/0x240 fs/splice.c:797 > splice_from_pipe_feed fs/splice.c:503 [inline] > __splice_from_pipe+0x38b/0x7c0 fs/splice.c:627 > splice_from_pipe+0x1ec/0x340 fs/splice.c:662 > default_file_splice_write+0x3c/0x90 fs/splice.c:809 > do_splice_from fs/splice.c:851 [inline] > do_splice+0x64a/0x1430 fs/splice.c:1147 > __do_sys_splice fs/splice.c:1414 [inline] > __se_sys_splice fs/splice.c:1394 [inline] > __x64_sys_splice+0x2c1/0x330 fs/splice.c:1394 > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x445ad9 > Code: e8 5c b7 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff > ff 0f 83 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007f18e3f71cd8 EFLAGS: 00000216 ORIG_RAX: 0000000000000113 > RAX: ffffffffffffffda RBX: 00000000006dac78 RCX: 0000000000445ad9 > RDX: 000000000000000a RSI: 0000000000000000 RDI: 0000000000000007 > RBP: 00000000006dac70 R08: 000100000000000a R09: 0000000000000007 > R10: 0000000000000000 R11: 0000000000000216 R12: 00000000006dac7c > R13: 00007ffde0706e9f R14: 00007f18e3f729c0 R15: 00000000006dad4c > This looks like a false positive because lockdep is not aware of s_stack_depth of the file (fs) associated with the pipe. HOWEVER, because overlayfs calls do_splice_direct() on copy up, it is important to make sure that higher layer do_splice_direct() cannot recursively trigger copy up. At this time, overlayfs does the copy up on open for write, so any higher layer do_splice_direct() will already get an out file that has been copied up, but with future plans for "lazy copy up on first write", we need to be careful. Thanks, Amir.
