linux-kernel - Re: [PATCH -next] ext4: fix use-after-free in ext4_rename_dir

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Date:   Fri, 13 May 2022 17:13:47 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ye Bin <yebin10@...wei.com>
Cc:     adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, jack@...e.cz, lczerner@...hat.com
Subject: Re: [PATCH -next] ext4: fix use-after-free in ext4_rename_dir_prepare

On Thu, Apr 14, 2022 at 10:52:23AM +0800, Ye Bin wrote:
> We got issue as follows:
> EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue
> ext4_get_first_dir_block: bh->b_data=0xffff88810bee6000 len=34478
> ext4_get_first_dir_block: *parent_de=0xffff88810beee6ae bh->b_data=0xffff88810bee6000
> ext4_rename_dir_prepare: [1] parent_de=0xffff88810beee6ae
> ==================================================================
> BUG: KASAN: use-after-free in ext4_rename_dir_prepare+0x152/0x220
> Read of size 4 at addr ffff88810beee6ae by task rep/1895
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index e37da8d5cd0c..2f78544b1d47 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -3463,9 +3466,28 @@ static struct buffer_head *ext4_get_first_dir_block(handle_t *handle,
>  			*retval = PTR_ERR(bh);
>  			return NULL;
>  		}
> -		*parent_de = ext4_next_entry(
> -					(struct ext4_dir_entry_2 *)bh->b_data,
> -					inode->i_sb->s_blocksize);
> +
> +		de = (struct ext4_dir_entry_2 *) bh->b_data;
> +		if (ext4_check_dir_entry(inode, NULL, de, bh, bh->b_data,
> +					 bh->b_size, 0) ||
> +		    le32_to_cpu(de->inode) != inode->i_ino ||
> +		    strcmp(".", de->name)) {
> +			ext4_warning_inode(inode, "directory missing '.'");

I think we should be calling ext4_error_inode()?  If the directory is
missing '.' or '..' below, the file system is corrupt, so we probably
should mark the file system as inconsistent, so that e2fsck can fix
the file system.

					- Ted