linux-ext4 - Re: [PATCH v2] ext4: fix bug for rename with RENAME

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Date:   Wed, 30 Dec 2020 11:29:14 +0800
From:   yangerkun <yangerkun@...wei.com>
To:     Theodore Ts'o <tytso@....edu>
CC:     <linux-ext4@...r.kernel.org>, <adilger.kernel@...ger.ca>,
        <jack@...e.cz>, <yi.zhang@...wei.com>, <lihaotian9@...wei.com>,
        <lutianxiong@...wei.com>, <linfeilong@...wei.com>
Subject: Re: [PATCH v2] ext4: fix bug for rename with RENAME_WHITEOUT

在 2020/12/30 6:24, Theodore Ts'o 写道:
> On Tue, Dec 29, 2020 at 05:02:08PM +0800, yangerkun wrote:
>> ext4_rename will create a special inode for whiteout and use this 'ino'
>> to replace the source file's dir entry 'ino'. Once error happens
>> latter(small ext4 img, and consume all space, so the rename with dst
>> path not exist will fail due to the ENOSPC return from ext4_add_entry in
>> ext4_rename), the cleanup do drop the nlink for whiteout, but forget to
>> restore 'ino' with source file. This will lead to "deleted inode
>> referenced".
> 
> Could you sendhave instructions how to reproduce this failure?  Many thanks!!

Hi,

Follow step will reproduce it easily!

cd /dev/shm
mkdir test/
fallocate -l 128M img
mkfs.ext4 -b 1024 img
mount img test/
dd if=/dev/zero of=test/foo bs=1M count=128
mkdir test/dir/ && cd test/dir/
for ((i=0;i<1000;i++)); do touch file$i; done # consume all block
cd ~ && renameat2(AT_FDCWD, /dev/shm/test/dir/file1, AT_FDCWD, 
/dev/shm/test/dir/dst_file, RENAME_WHITEOUT) # ext4_add_entry in 
ext4_rename will return ENOSPC!!
cd /dev/shm/ && mount img test/ && ls -li test/dir/file1
We will get the output:
"ls: cannot access 'test/dir/file1': Structure needs cleaning"
and the dmesg show:
"EXT4-fs error (device loop0): ext4_lookup:1626: inode #2049: comm ls: 
deleted inode referenced: 139"

static int ext4_rename(...)
{
	...
	whiteout = ext4_whiteout_for_rename(&old, credits, &handle);
	...
	retval = ext4_setent(handle, &old, whiteout->i_ino, EXT4_FT_CHRDEV); // 
will replace dir entry with
	...
	if (!new.bh) {
		retval = ext4_add_entry(handle, new.dentry, old.inode); // will fail 
with ENOSPC
		if (retval)
			goto end_rename;
	...
end_rename:
	...
	if (whiteout) { // forget to restore the dir entry's ino
		if (retval)
			drop_nlink(whiteout);
		unlock_new_inode(whiteout);
		iput(whiteout);
	}
	...
}

Thanks,
Kun.

> 
>        	  	   		    - Ted
> .
>