Re: [PATCH] ext4: fix task hung in ext4_xattr_delete_inode

[Jan Kara]

On Tue 10-01-23 12:27:09, Baokun Li wrote:
> Syzbot reported a hung task problem:
> ==================================================================
> INFO: task syz-executor232:5073 blocked for more than 143 seconds.
>       Not tainted 6.2.0-rc2-syzkaller-00024-g512dee0c00ad #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:syz-exec232 state:D stack:21024 pid:5073 ppid:5072 flags:0x00004004
> Call Trace:
>  <TASK>
>  context_switch kernel/sched/core.c:5244 [inline]
>  __schedule+0x995/0xe20 kernel/sched/core.c:6555
>  schedule+0xcb/0x190 kernel/sched/core.c:6631
>  __wait_on_freeing_inode fs/inode.c:2196 [inline]
>  find_inode_fast+0x35a/0x4c0 fs/inode.c:950
>  iget_locked+0xb1/0x830 fs/inode.c:1273
>  __ext4_iget+0x22e/0x3ed0 fs/ext4/inode.c:4861
>  ext4_xattr_inode_iget+0x68/0x4e0 fs/ext4/xattr.c:389
>  ext4_xattr_inode_dec_ref_all+0x1a7/0xe50 fs/ext4/xattr.c:1148
>  ext4_xattr_delete_inode+0xb04/0xcd0 fs/ext4/xattr.c:2880
>  ext4_evict_inode+0xd7c/0x10b0 fs/ext4/inode.c:296
>  evict+0x2a4/0x620 fs/inode.c:664
>  ext4_orphan_cleanup+0xb60/0x1340 fs/ext4/orphan.c:474
>  __ext4_fill_super fs/ext4/super.c:5516 [inline]
>  ext4_fill_super+0x81cd/0x8700 fs/ext4/super.c:5644
>  get_tree_bdev+0x400/0x620 fs/super.c:1282
>  vfs_get_tree+0x88/0x270 fs/super.c:1489
>  do_new_mount+0x289/0xad0 fs/namespace.c:3145
>  do_mount fs/namespace.c:3488 [inline]
>  __do_sys_mount fs/namespace.c:3697 [inline]
>  __se_sys_mount+0x2d3/0x3c0 fs/namespace.c:3674
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7fa5406fd5ea
> RSP: 002b:00007ffc7232f968 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fa5406fd5ea
> RDX: 0000000020000440 RSI: 0000000020000000 RDI: 00007ffc7232f970
> RBP: 00007ffc7232f970 R08: 00007ffc7232f9b0 R09: 0000000000000432
> R10: 0000000000804a03 R11: 0000000000000202 R12: 0000000000000004
> R13: 0000555556a7a2c0 R14: 00007ffc7232f9b0 R15: 0000000000000000
>  </TASK>
> ==================================================================
> 
> The problem is that the inode contains an xattr entry with ea_inum of 15
> when cleaning up an orphan inode <15>. When evict inode <15>, the reference
> counting of the corresponding EA inode is decreased. When EA inode <15> is
> found by find_inode_fast() in __ext4_iget(), it is found that the EA inode
> holds the I_FREEING flag and waits for the EA inode to complete deletion.
> As a result, when inode <15> is being deleted, we wait for inode <15> to
> complete the deletion, resulting in an infinite loop and triggering Hung
> Task. To solve this problem, we only need to check whether the ino of EA
> inode and parent is the same before getting EA inode.
> 
> Link: https://syzkaller.appspot.com/bug?extid=77d6fcc37bbb92f26048
> Reported-by: syzbot+77d6fcc37bbb92f26048@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> ---
>  fs/ext4/xattr.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 7decaaf27e82..9ff8fcf78bb8 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -386,6 +386,13 @@ static int ext4_xattr_inode_iget(struct inode *parent, unsigned long ea_ino,
>  	struct inode *inode;
>  	int err;
>  

Perhaps add a comment here like:

	/*
	 * We have to check for this corruption early as otherwise
	 * iget_locked() could wait indefinitely for the state of our
	 * parent inode.
	 */

> +	if (parent->i_ino == ea_ino) {
> +		ext4_error(parent->i_sb,
> +			   "Parent and EA inode have the same ino %lu", ea_ino);
> +		err = -EUCLEAN;
			^^ I prefer -EFSCORRUPTED here. It is the same
value but more descriptive name :).

> +		goto error;
		^^ Just "return err" here. This will try to iput()
uninitialized pointer.

								Honza

-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR