[PATCH] ext4: fix deadlock in ext4_xattr_inode_iget
From: Edward Adam Davis
Date: Wed Apr 03 2024 - 22:00:32 EST
[Syzbot reported]
WARNING: possible circular locking dependency detected
6.8.0-syzkaller-08951-gfe46a7dd189e #0 Not tainted
------------------------------------------------------
syz-executor545/5275 is trying to acquire lock:
ffff888077730400 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:793 [inline]
ffff888077730400 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}, at: ext4_xattr_inode_iget+0x173/0x440 fs/ext4/xattr.c:461
but task is already holding lock:
ffff888077730c88 (&ei->i_data_sem/3){++++}-{3:3}, at: ext4_setattr+0x1ba0/0x29d0 fs/ext4/inode.c:5417
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&ei->i_data_sem/3){++++}-{3:3}:
down_write+0x3a/0x50 kernel/locking/rwsem.c:1579
ext4_update_i_disksize fs/ext4/ext4.h:3383 [inline]
ext4_xattr_inode_write fs/ext4/xattr.c:1446 [inline]
ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1594 [inline]
ext4_xattr_set_entry+0x3a14/0x3cf0 fs/ext4/xattr.c:1719
ext4_xattr_ibody_set+0x126/0x380 fs/ext4/xattr.c:2287
ext4_xattr_set_handle+0x98d/0x1480 fs/ext4/xattr.c:2444
ext4_xattr_set+0x149/0x380 fs/ext4/xattr.c:2558
__vfs_setxattr+0x176/0x1e0 fs/xattr.c:200
__vfs_setxattr_noperm+0x127/0x5e0 fs/xattr.c:234
__vfs_setxattr_locked+0x182/0x260 fs/xattr.c:295
vfs_setxattr+0x146/0x350 fs/xattr.c:321
do_setxattr+0x146/0x170 fs/xattr.c:629
setxattr+0x15d/0x180 fs/xattr.c:652
path_setxattr+0x179/0x1e0 fs/xattr.c:671
__do_sys_lsetxattr fs/xattr.c:694 [inline]
__se_sys_lsetxattr fs/xattr.c:690 [inline]
__x64_sys_lsetxattr+0xc1/0x160 fs/xattr.c:690
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xd5/0x260 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x6d/0x75
-> #0 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2478/0x3b30 kernel/locking/lockdep.c:5137
lock_acquire kernel/locking/lockdep.c:5754 [inline]
lock_acquire+0x1b1/0x540 kernel/locking/lockdep.c:5719
down_write+0x3a/0x50 kernel/locking/rwsem.c:1579
inode_lock include/linux/fs.h:793 [inline]
ext4_xattr_inode_iget+0x173/0x440 fs/ext4/xattr.c:461
ext4_xattr_inode_get+0x16c/0x870 fs/ext4/xattr.c:535
ext4_xattr_move_to_block fs/ext4/xattr.c:2640 [inline]
ext4_xattr_make_inode_space fs/ext4/xattr.c:2742 [inline]
ext4_expand_extra_isize_ea+0x1367/0x1ae0 fs/ext4/xattr.c:2834
__ext4_expand_extra_isize+0x346/0x480 fs/ext4/inode.c:5789
ext4_try_to_expand_extra_isize fs/ext4/inode.c:5832 [inline]
__ext4_mark_inode_dirty+0x55a/0x860 fs/ext4/inode.c:5910
ext4_setattr+0x1c14/0x29d0 fs/ext4/inode.c:5420
notify_change+0x745/0x11c0 fs/attr.c:497
do_truncate+0x15c/0x220 fs/open.c:65
handle_truncate fs/namei.c:3300 [inline]
do_open fs/namei.c:3646 [inline]
path_openat+0x24b9/0x2990 fs/namei.c:3799
do_filp_open+0x1dc/0x430 fs/namei.c:3826
do_sys_openat2+0x17a/0x1e0 fs/open.c:1406
do_sys_open fs/open.c:1421 [inline]
__do_sys_openat fs/open.c:1437 [inline]
__se_sys_openat fs/open.c:1432 [inline]
__x64_sys_openat+0x175/0x210 fs/open.c:1432
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xd5/0x260 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x6d/0x75
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&ei->i_data_sem/3);
lock(&ea_inode->i_rwsem#8/1);
lock(&ei->i_data_sem/3);
lock(&ea_inode->i_rwsem#8/1);
*** DEADLOCK ***
[Fix]
According to mark inode dirty context, it does not need to be protected by lock
i_data_sem, and if it is protected by i_data_sem, a deadlock will occur.
Reported-by: syzbot+ee72b9a7aad1e5a77c5c@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
fs/ext4/inode.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 537803250ca9..d2cbe3dddfab 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5417,6 +5417,7 @@ int ext4_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
down_write(&EXT4_I(inode)->i_data_sem);
old_disksize = EXT4_I(inode)->i_disksize;
EXT4_I(inode)->i_disksize = attr->ia_size;
+ up_write(&EXT4_I(inode)->i_data_sem);
rc = ext4_mark_inode_dirty(handle, inode);
if (!error)
error = rc;
@@ -5425,6 +5426,7 @@ int ext4_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
* with i_disksize to avoid races with writeback code
* running ext4_wb_update_i_disksize().
*/
+ down_write(&EXT4_I(inode)->i_data_sem);
if (!error)
i_size_write(inode, attr->ia_size);
else
--
2.43.0