Re: [syzbot] possible deadlock in ext4_xattr_get

From: syzbot
Date: Mon Aug 08 2022 - 07:26:21 EST

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in ext4_xattr_get

loop0: detected capacity change from 0 to 512
EXT4-fs (loop0): mounted filesystem without journal. Quota mode: none.
======================================================
WARNING: possible circular locking dependency detected
5.19.0-rc4-next-20220628-syzkaller-dirty #0 Not tainted
------------------------------------------------------
syz-executor.0/4081 is trying to acquire lock:
ffff888073393cf8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_xattr_get+0x14e/0xa10 fs/ext4/xattr.c:650

but task is already holding lock:
ffff888073394030 (&ea_inode->i_rwsem#9/1){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:761 [inline]
ffff888073394030 (&ea_inode->i_rwsem#9/1){+.+.}-{3:3}, at: chown_common+0x364/0x710 fs/open.c:727

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&ea_inode->i_rwsem#9/1){+.+.}-{3:3}:
down_write+0x90/0x150 kernel/locking/rwsem.c:1542
inode_lock include/linux/fs.h:761 [inline]
ext4_xattr_inode_write fs/ext4/xattr.c:1391 [inline]
ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1529 [inline]
ext4_xattr_set_entry+0x2ec5/0x3800 fs/ext4/xattr.c:1653
ext4_xattr_ibody_set+0x78/0x2b0 fs/ext4/xattr.c:2206
ext4_xattr_set_handle+0x964/0x1500 fs/ext4/xattr.c:2363
ext4_xattr_set+0x13a/0x340 fs/ext4/xattr.c:2476
__vfs_setxattr+0x115/0x180 fs/xattr.c:182
__vfs_setxattr_noperm+0x125/0x5f0 fs/xattr.c:216
__vfs_setxattr_locked+0x1cf/0x260 fs/xattr.c:277
vfs_setxattr+0x13f/0x330 fs/xattr.c:303
setxattr+0x146/0x160 fs/xattr.c:611
path_setxattr+0x197/0x1c0 fs/xattr.c:630
__do_sys_setxattr fs/xattr.c:646 [inline]
__se_sys_setxattr fs/xattr.c:642 [inline]
__x64_sys_setxattr+0xc0/0x160 fs/xattr.c:642
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+0x46/0xb0

-> #0 (&ei->xattr_sem){++++}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5665 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630
down_read+0x98/0x440 kernel/locking/rwsem.c:1489
ext4_xattr_get+0x14e/0xa10 fs/ext4/xattr.c:650
__vfs_getxattr+0xd9/0x140 fs/xattr.c:401
cap_inode_need_killpriv+0x3c/0x60 security/commoncap.c:301
security_inode_need_killpriv+0x40/0x90 security/security.c:1420
notify_change+0x6e7/0x1440 fs/attr.c:351
chown_common+0x61b/0x710 fs/open.c:734
do_fchownat+0x126/0x1e0 fs/open.c:765
__do_sys_fchownat fs/open.c:780 [inline]
__se_sys_fchownat fs/open.c:777 [inline]
__x64_sys_fchownat+0xba/0x150 fs/open.c:777
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+0x46/0xb0

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&ea_inode->i_rwsem#9/1);
lock(&ei->xattr_sem);
lock(&ea_inode->i_rwsem#9/1);
lock(&ei->xattr_sem);

*** DEADLOCK ***

2 locks held by syz-executor.0/4081:
#0: ffff88807a612460 (sb_writers#4){.+.+}-{0:0}, at: do_fchownat+0x101/0x1e0 fs/open.c:762
#1: ffff888073394030 (&ea_inode->i_rwsem#9/1){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:761 [inline]
#1: ffff888073394030 (&ea_inode->i_rwsem#9/1){+.+.}-{3:3}, at: chown_common+0x364/0x710 fs/open.c:727

stack backtrace:
CPU: 0 PID: 4081 Comm: syz-executor.0 Not tainted 5.19.0-rc4-next-20220628-syzkaller-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5665 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630
down_read+0x98/0x440 kernel/locking/rwsem.c:1489
ext4_xattr_get+0x14e/0xa10 fs/ext4/xattr.c:650
__vfs_getxattr+0xd9/0x140 fs/xattr.c:401
cap_inode_need_killpriv+0x3c/0x60 security/commoncap.c:301
security_inode_need_killpriv+0x40/0x90 security/security.c:1420
notify_change+0x6e7/0x1440 fs/attr.c:351
chown_common+0x61b/0x710 fs/open.c:734
do_fchownat+0x126/0x1e0 fs/open.c:765
__do_sys_fchownat fs/open.c:780 [inline]
__se_sys_fchownat fs/open.c:777 [inline]
__x64_sys_fchownat+0xba/0x150 fs/open.c:777
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+0x46/0xb0
RIP: 0033:0x7febbbc89209
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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:00007febbcdc0168 EFLAGS: 00000246 ORIG_RAX: 0000000000000104
RAX: ffffffffffffffda RBX: 00007febbbd9bf60 RCX: 00007febbbc89209
RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000000000005
RBP: 00007febbbce3161 R08: 0000000000001000 R09: 0000000000000000
R10: 000000000000ee01 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd5bc171ff R14: 00007febbcdc0300 R15: 0000000000022000
</TASK>


Tested on:

commit: cb71b93c Add linux-next specific files for 20220628
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=13ec5671080000
kernel config: https://syzkaller.appspot.com/x/.config?x=badbc1adb2d582eb
dashboard link: https://syzkaller.appspot.com/bug?extid=62120febbd1ee3c3c860
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch: https://syzkaller.appspot.com/x/patch.diff?x=162cf612080000