linux-kernel - Re: [syzbot] [ext4?] possible deadlock in ext4_xattr_set

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Message-ID: <0000000000000c53dd05faf94183@google.com>
Date:   Fri, 05 May 2023 14:48:48 -0700
From:   syzbot <syzbot+edce54daffee36421b4c@...kaller.appspotmail.com>
To:     adilger.kernel@...ger.ca, dvyukov@...gle.com, jack@...e.cz,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        tytso@....edu
Subject: Re: [syzbot] [ext4?] possible deadlock in ext4_xattr_set_handle (3)

syzbot has found a reproducer for the following issue on:

HEAD commit:    14f8db1c0f9a 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=1663f338280000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a837a8ba7e88bb45
dashboard link: https://syzkaller.appspot.com/bug?extid=edce54daffee36421b4c
compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17595ed4280000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16e85322280000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ad6ce516eed3/disk-14f8db1c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1f38c2cc7667/vmlinux-14f8db1c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d795115eee39/Image-14f8db1c.gz.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/092c100a5922/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+edce54daffee36421b4c@...kaller.appspotmail.com

loop0: detected capacity change from 0 to 512
EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 without journal. Quota mode: writeback.
======================================================
WARNING: possible circular locking dependency detected
6.3.0-rc7-syzkaller-g14f8db1c0f9a #0 Not tainted
------------------------------------------------------
syz-executor392/5925 is trying to acquire lock:
ffff0000e0dbb2f0 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:155 [inline]
ffff0000e0dbb2f0 (&ei->xattr_sem){++++}-{3:3}, at: ext4_xattr_set_handle+0x1e0/0x12d8 fs/ext4/xattr.c:2373

but task is already holding lock:
ffff0000e0dbb628 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:758 [inline]
ffff0000e0dbb628 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}, at: vfs_setxattr+0x17c/0x344 fs/xattr.c:323

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}:
       down_write+0x50/0xc0 kernel/locking/rwsem.c:1573
       inode_lock include/linux/fs.h:758 [inline]
       ext4_xattr_inode_create fs/ext4/xattr.c:1525 [inline]
       ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1608 [inline]
       ext4_xattr_set_entry+0x2394/0x2c3c fs/ext4/xattr.c:1737
       ext4_xattr_block_set+0x8e0/0x2cc4 fs/ext4/xattr.c:2043
       ext4_xattr_set_handle+0xb2c/0x12d8 fs/ext4/xattr.c:2458
       ext4_xattr_set+0x1e0/0x354 fs/ext4/xattr.c:2560
       ext4_xattr_trusted_set+0x4c/0x64 fs/ext4/xattr_trusted.c:38
       __vfs_setxattr+0x3d8/0x400 fs/xattr.c:203
       __vfs_setxattr_noperm+0x110/0x528 fs/xattr.c:237
       __vfs_setxattr_locked+0x1ec/0x218 fs/xattr.c:298
       vfs_setxattr+0x1a8/0x344 fs/xattr.c:324
       do_setxattr fs/xattr.c:609 [inline]
       setxattr+0x208/0x29c fs/xattr.c:632
       path_setxattr+0x17c/0x258 fs/xattr.c:651
       __do_sys_setxattr fs/xattr.c:667 [inline]
       __se_sys_setxattr fs/xattr.c:663 [inline]
       __arm64_sys_setxattr+0xbc/0xd8 fs/xattr.c:663
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x64/0x198 arch/arm64/kernel/syscall.c:193
       el0_svc+0x4c/0x15c arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:591

-> #0 (&ei->xattr_sem){++++}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3098 [inline]
       check_prevs_add kernel/locking/lockdep.c:3217 [inline]
       validate_chain kernel/locking/lockdep.c:3832 [inline]
       __lock_acquire+0x3338/0x764c kernel/locking/lockdep.c:5056
       lock_acquire+0x238/0x718 kernel/locking/lockdep.c:5669
       down_write+0x50/0xc0 kernel/locking/rwsem.c:1573
       ext4_write_lock_xattr fs/ext4/xattr.h:155 [inline]
       ext4_xattr_set_handle+0x1e0/0x12d8 fs/ext4/xattr.c:2373
       ext4_xattr_set+0x1e0/0x354 fs/ext4/xattr.c:2560
       ext4_xattr_trusted_set+0x4c/0x64 fs/ext4/xattr_trusted.c:38
       __vfs_setxattr+0x3d8/0x400 fs/xattr.c:203
       __vfs_setxattr_noperm+0x110/0x528 fs/xattr.c:237
       __vfs_setxattr_locked+0x1ec/0x218 fs/xattr.c:298
       vfs_setxattr+0x1a8/0x344 fs/xattr.c:324
       do_setxattr fs/xattr.c:609 [inline]
       setxattr+0x208/0x29c fs/xattr.c:632
       path_setxattr+0x17c/0x258 fs/xattr.c:651
       __do_sys_setxattr fs/xattr.c:667 [inline]
       __se_sys_setxattr fs/xattr.c:663 [inline]
       __arm64_sys_setxattr+0xbc/0xd8 fs/xattr.c:663
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x64/0x198 arch/arm64/kernel/syscall.c:193
       el0_svc+0x4c/0x15c arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:591

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ea_inode->i_rwsem#8/1);
                               lock(&ei->xattr_sem);
                               lock(&ea_inode->i_rwsem#8/1);
  lock(&ei->xattr_sem);

 *** DEADLOCK ***

2 locks held by syz-executor392/5925:
 #0: ffff0000d80e6460 (sb_writers#3){.+.+}-{0:0}, at: mnt_want_write+0x44/0x9c fs/namespace.c:394
 #1: ffff0000e0dbb628 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:758 [inline]
 #1: ffff0000e0dbb628 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}, at: vfs_setxattr+0x17c/0x344 fs/xattr.c:323

stack backtrace:
CPU: 1 PID: 5925 Comm: syz-executor392 Not tainted 6.3.0-rc7-syzkaller-g14f8db1c0f9a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
Call trace:
 dump_backtrace+0x1b8/0x1e4 arch/arm64/kernel/stacktrace.c:233
 show_stack+0x2c/0x44 arch/arm64/kernel/stacktrace.c:240
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd0/0x124 lib/dump_stack.c:106
 dump_stack+0x1c/0x28 lib/dump_stack.c:113
 print_circular_bug+0x150/0x1b8 kernel/locking/lockdep.c:2056
 check_noncircular+0x2cc/0x378 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3098 [inline]
 check_prevs_add kernel/locking/lockdep.c:3217 [inline]
 validate_chain kernel/locking/lockdep.c:3832 [inline]
 __lock_acquire+0x3338/0x764c kernel/locking/lockdep.c:5056
 lock_acquire+0x238/0x718 kernel/locking/lockdep.c:5669
 down_write+0x50/0xc0 kernel/locking/rwsem.c:1573
 ext4_write_lock_xattr fs/ext4/xattr.h:155 [inline]
 ext4_xattr_set_handle+0x1e0/0x12d8 fs/ext4/xattr.c:2373
 ext4_xattr_set+0x1e0/0x354 fs/ext4/xattr.c:2560
 ext4_xattr_trusted_set+0x4c/0x64 fs/ext4/xattr_trusted.c:38
 __vfs_setxattr+0x3d8/0x400 fs/xattr.c:203
 __vfs_setxattr_noperm+0x110/0x528 fs/xattr.c:237
 __vfs_setxattr_locked+0x1ec/0x218 fs/xattr.c:298
 vfs_setxattr+0x1a8/0x344 fs/xattr.c:324
 do_setxattr fs/xattr.c:609 [inline]
 setxattr+0x208/0x29c fs/xattr.c:632
 path_setxattr+0x17c/0x258 fs/xattr.c:651
 __do_sys_setxattr fs/xattr.c:667 [inline]
 __se_sys_setxattr fs/xattr.c:663 [inline]
 __arm64_sys_setxattr+0xbc/0xd8 fs/xattr.c:663
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x64/0x198 arch/arm64/kernel/syscall.c:193
 el0_svc+0x4c/0x15c arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:591


---
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#syz test: git://repo/address.git branch-or-commit-hash
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