[syzbot] [overlayfs?] possible deadlock in ovl_copy_up_flags (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    4b4362973b6f Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=1292dc2e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a834c6344141a58b
dashboard link: https://syzkaller.appspot.com/bug?extid=b754bc5f4c7fddac5253
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: arm64

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f69f86c90ee5/disk-4b436297.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/79fa7b33aaab/vmlinux-4b436297.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ef080156d0de/Image-4b436297.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b754bc5f4c7fddac5253@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.344/6315 is trying to acquire lock:
ffff0000cbc50410 (sb_writers#3){.+.+}-{0:0}, at: ovl_do_copy_up fs/overlayfs/copy_up.c:977 [inline]
ffff0000cbc50410 (sb_writers#3){.+.+}-{0:0}, at: ovl_copy_up_one fs/overlayfs/copy_up.c:1189 [inline]
ffff0000cbc50410 (sb_writers#3){.+.+}-{0:0}, at: ovl_copy_up_flags+0x980/0x28a4 fs/overlayfs/copy_up.c:1243

but task is already holding lock:
ffff0000f25fdcd8 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_inode_lock_interruptible fs/overlayfs/overlayfs.h:705 [inline]
ffff0000f25fdcd8 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_copy_up_start+0x58/0x264 fs/overlayfs/util.c:735

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&ovl_i_lock_key[depth]){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x160/0xef8 kernel/locking/mutex.c:820
       mutex_lock_interruptible_nested+0x24/0x30 kernel/locking/mutex.c:898
       ovl_inode_lock_interruptible fs/overlayfs/overlayfs.h:705 [inline]
       ovl_copy_up_start+0x58/0x264 fs/overlayfs/util.c:735
       ovl_copy_up_one fs/overlayfs/copy_up.c:1182 [inline]
       ovl_copy_up_flags+0x768/0x28a4 fs/overlayfs/copy_up.c:1243
       ovl_copy_up+0x24/0x34 fs/overlayfs/copy_up.c:1282
       ovl_link+0x8c/0x26c fs/overlayfs/dir.c:774
       vfs_link+0x40c/0x580 fs/namei.c:5774
       filename_linkat+0x224/0x478 fs/namei.c:5842
       __do_sys_linkat fs/namei.c:5868 [inline]
       __se_sys_linkat fs/namei.c:5863 [inline]
       __arm64_sys_linkat+0xe8/0x118 fs/namei.c:5863
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:121
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:140
       el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:740
       el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:759
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

-> #1 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}:
       down_write+0x50/0xc0 kernel/locking/rwsem.c:1625
       inode_lock include/linux/fs.h:1029 [inline]
       lock_two_nondirectories+0xc4/0x148 fs/inode.c:1254
       ext4_move_extents+0x194/0x3580 fs/ext4/move_extent.c:589
       __ext4_ioctl fs/ext4/ioctl.c:1657 [inline]
       ext4_ioctl+0x2a14/0x4234 fs/ext4/ioctl.c:1922
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:121
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:140
       el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:740
       el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:759
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

-> #0 (sb_writers#3){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x1780/0x2f44 kernel/locking/lockdep.c:5237
       lock_acquire+0x140/0x368 kernel/locking/lockdep.c:5868
       percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
       percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
       __sb_start_write include/linux/fs/super.h:19 [inline]
       sb_start_write include/linux/fs/super.h:125 [inline]
       ovl_start_write+0xf0/0x324 fs/overlayfs/util.c:32
       ovl_do_copy_up fs/overlayfs/copy_up.c:977 [inline]
       ovl_copy_up_one fs/overlayfs/copy_up.c:1189 [inline]
       ovl_copy_up_flags+0x980/0x28a4 fs/overlayfs/copy_up.c:1243
       ovl_copy_up+0x24/0x34 fs/overlayfs/copy_up.c:1282
       ovl_xattr_set+0x284/0x47c fs/overlayfs/xattrs.c:54
       ovl_other_xattr_set+0x50/0x68 fs/overlayfs/xattrs.c:224
       __vfs_setxattr+0x130/0x17c fs/xattr.c:218
       __vfs_setxattr_noperm+0x120/0x5c4 fs/xattr.c:252
       __vfs_setxattr_locked+0x114/0x248 fs/xattr.c:313
       vfs_setxattr+0x150/0x2e0 fs/xattr.c:339
       do_setxattr+0xf8/0x190 fs/xattr.c:654
       filename_setxattr+0x134/0x1f8 fs/xattr.c:682
       path_setxattrat+0x200/0x2a8 fs/xattr.c:726
       __do_sys_setxattr fs/xattr.c:760 [inline]
       __se_sys_setxattr fs/xattr.c:756 [inline]
       __arm64_sys_setxattr+0xc0/0xdc fs/xattr.c:756
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:121
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:140
       el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:740
       el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:759
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

other info that might help us debug this:

Chain exists of:
  sb_writers#3 --> &ovl_i_mutex_key[depth] --> &ovl_i_lock_key[depth]

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ovl_i_lock_key[depth]);
                               lock(&ovl_i_mutex_key[depth]);
                               lock(&ovl_i_lock_key[depth]);
  rlock(sb_writers#3);

 *** DEADLOCK ***

3 locks held by syz.5.344/6315:
 #0: ffff0000f5150410 (sb_writers#15){.+.+}-{0:0}, at: mnt_want_write+0x44/0x9c fs/namespace.c:493
 #1: ffff0000f25fd960 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1029 [inline]
 #1: ffff0000f25fd960 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: vfs_setxattr+0x130/0x2e0 fs/xattr.c:338
 #2: ffff0000f25fdcd8 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_inode_lock_interruptible fs/overlayfs/overlayfs.h:705 [inline]
 #2: ffff0000f25fdcd8 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_copy_up_start+0x58/0x264 fs/overlayfs/util.c:735

stack backtrace:
CPU: 1 UID: 0 PID: 6315 Comm: syz.5.344 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 dump_stack+0x1c/0x28 lib/dump_stack.c:129
 print_circular_bug+0x328/0x330 kernel/locking/lockdep.c:2043
 check_noncircular+0x158/0x174 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x1780/0x2f44 kernel/locking/lockdep.c:5237
 lock_acquire+0x140/0x368 kernel/locking/lockdep.c:5868
 percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
 percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
 __sb_start_write include/linux/fs/super.h:19 [inline]
 sb_start_write include/linux/fs/super.h:125 [inline]
 ovl_start_write+0xf0/0x324 fs/overlayfs/util.c:32
 ovl_do_copy_up fs/overlayfs/copy_up.c:977 [inline]
 ovl_copy_up_one fs/overlayfs/copy_up.c:1189 [inline]
 ovl_copy_up_flags+0x980/0x28a4 fs/overlayfs/copy_up.c:1243
 ovl_copy_up+0x24/0x34 fs/overlayfs/copy_up.c:1282
 ovl_xattr_set+0x284/0x47c fs/overlayfs/xattrs.c:54
 ovl_other_xattr_set+0x50/0x68 fs/overlayfs/xattrs.c:224
 __vfs_setxattr+0x130/0x17c fs/xattr.c:218
 __vfs_setxattr_noperm+0x120/0x5c4 fs/xattr.c:252
 __vfs_setxattr_locked+0x114/0x248 fs/xattr.c:313
 vfs_setxattr+0x150/0x2e0 fs/xattr.c:339
 do_setxattr+0xf8/0x190 fs/xattr.c:654
 filename_setxattr+0x134/0x1f8 fs/xattr.c:682
 path_setxattrat+0x200/0x2a8 fs/xattr.c:726
 __do_sys_setxattr fs/xattr.c:760 [inline]
 __se_sys_setxattr fs/xattr.c:756 [inline]
 __arm64_sys_setxattr+0xc0/0xdc fs/xattr.c:756
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:740
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:759
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
EXT4-fs error (device loop5): ext4_find_dest_de:2050: inode #12: block 7: comm syz.5.344: bad entry in directory: rec_len is too small for name_len - offset=16, inode=14, rec_len=40, size=56 fake=0
EXT4-fs (loop5): Remounting filesystem read-only


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup