[syzbot] [kernfs?] possible deadlock in kernfs_fop_llseek

syzbot
2024-04-03T18:23:27Z

Hello,

syzbot found the following issue on:

HEAD commit: fe46a7dd189e Merge tag 'sound-6.9-rc1' of git://git.kernel..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=136eb2f6180000
kernel config: https://syzkaller.appspot.com/x/.config?x=4d90a36f0cab495a
dashboard link: https://syzkaller.appspot.com/bug?extid=9a5b0ced8b1bfb238b56
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17f1d93d180000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15c38139180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/72ab73815344/disk-fe46a7dd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2d6d6b0d7071/vmlinux-fe46a7dd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/48e275e5478b/bzImage-fe46a7dd.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9a5b0ced8b1bfb238b56@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.8.0-syzkaller-08951-gfe46a7dd189e #0 Not tainted
------------------------------------------------------
syz-executor250/5062 is trying to acquire lock:
ffff888022c36888 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_llseek+0x7e/0x2a0 fs/kernfs/file.c:867

but task is already holding lock:
ffff88807edeadd8 (&ovl_i_lock_key[depth]){+.+.}-{3:3}, at: ovl_inode_lock fs/overlayfs/overlayfs.h:649 [inline]
ffff88807edeadd8 (&ovl_i_lock_key[depth]){+.+.}-{3:3}, at: ovl_llseek+0x26b/0x470 fs/overlayfs/file.c:214

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&ovl_i_lock_key[depth]){+.+.}-{3:3}:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
ovl_inode_lock_interruptible fs/overlayfs/overlayfs.h:654 [inline]
ovl_nlink_start+0xdc/0x390 fs/overlayfs/util.c:1162
ovl_do_remove+0x1fa/0xd90 fs/overlayfs/dir.c:893
vfs_rmdir+0x367/0x4c0 fs/namei.c:4209
do_rmdir+0x3b5/0x580 fs/namei.c:4268
__do_sys_rmdir fs/namei.c:4287 [inline]
__se_sys_rmdir fs/namei.c:4285 [inline]
__x64_sys_rmdir+0x49/0x60 fs/namei.c:4285
do_syscall_64+0xfb/0x240
entry_SYSCALL_64_after_hwframe+0x6d/0x75

-> #1 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
down_read+0xb1/0xa40 kernel/locking/rwsem.c:1526
inode_lock_shared include/linux/fs.h:803 [inline]
lookup_slow+0x45/0x70 fs/namei.c:1708
walk_component+0x2e1/0x410 fs/namei.c:2004
lookup_last fs/namei.c:2461 [inline]
path_lookupat+0x16f/0x450 fs/namei.c:2485
filename_lookup+0x256/0x610 fs/namei.c:2514
kern_path+0x35/0x50 fs/namei.c:2622
lookup_bdev+0xc5/0x290 block/bdev.c:1072
resume_store+0x1a0/0x710 kernel/power/hibernate.c:1235
kernfs_fop_write_iter+0x3a4/0x500 fs/kernfs/file.c:334
call_write_iter include/linux/fs.h:2108 [inline]
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0xa84/0xcb0 fs/read_write.c:590
ksys_write+0x1a0/0x2c0 fs/read_write.c:643
do_syscall_64+0xfb/0x240
entry_SYSCALL_64_after_hwframe+0x6d/0x75

-> #0 (&of->mutex){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
kernfs_fop_llseek+0x7e/0x2a0 fs/kernfs/file.c:867
ovl_llseek+0x314/0x470 fs/overlayfs/file.c:218
vfs_llseek fs/read_write.c:289 [inline]
ksys_lseek fs/read_write.c:302 [inline]
__do_sys_lseek fs/read_write.c:313 [inline]
__se_sys_lseek fs/read_write.c:311 [inline]
__x64_sys_lseek+0x153/0x1e0 fs/read_write.c:311
do_syscall_64+0xfb/0x240
entry_SYSCALL_64_after_hwframe+0x6d/0x75

other info that might help us debug this:

Chain exists of:
&of->mutex --> &ovl_i_mutex_dir_key[depth] --> &ovl_i_lock_key[depth]

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&ovl_i_lock_key[depth]);
lock(&ovl_i_mutex_dir_key[depth]);
lock(&ovl_i_lock_key[depth]);
lock(&of->mutex);

*** DEADLOCK ***

1 lock held by syz-executor250/5062:
#0: ffff88807edeadd8 (&ovl_i_lock_key[depth]){+.+.}-{3:3}, at: ovl_inode_lock fs/overlayfs/overlayfs.h:649 [inline]
#0: ffff88807edeadd8 (&ovl_i_lock_key[depth]){+.+.}-{3:3}, at: ovl_llseek+0x26b/0x470 fs/overlayfs/file.c:214

stack backtrace:
CPU: 1 PID: 5062 Comm: syz-executor250 Not tainted 6.8.0-syzkaller-08951-gfe46a7dd189e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
kernfs_fop_llseek+0x7e/0x2a0 fs/kernfs/file.c:867
ovl_llseek+0x314/0x470 fs/overlayfs/file.c:218
vfs_llseek fs/read_write.c:289 [inline]
ksys_lseek fs/read_write.c:302 [inline]
__do_sys_lseek fs/read_write.c:313 [inline]
__se_sys_lseek fs/read_write.c:311 [inline]
__x64_sys_lseek+0x153/0x1e0 fs/read_write.c:311
do_syscall_64+0xfb/0x240
entry_SYSCALL_64_after_hwframe+0x6d/0x75
RIP: 0033:0x7f0e2bdfd219
Code: 48 83 c4 28 c3 e8 67 17 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd2f80f3f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000008
RAX: ffffffffffffffda RBX: 00007ffd2f80f400 RCX: 00007f0e2bdfd219
RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007ffd2f80f408 R08: 00007f0e2bdca000 R09: 00007f0e2bdca000
R10: 00007f0e2bdca000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd2f80f668 R14: 0000000000000001 R15: 0000000000000001

---
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