Re: [PATCH] ocfs2: validate inline dir size in ocfs2_dir_foreach_blk_id

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 4/10/26 2:22 PM, ZhengYuan Huang wrote:
> [BUG]
> A crafted inline-data directory can set i_size larger than id_count.
> readdir then walks past data->id_data and KASAN reports:
> 
> BUG: KASAN: use-after-free in ocfs2_check_dir_entry.isra.0+0x31f/0x370 fs/ocfs2/dir.c:305
> Read of size 2 at addr ffff8880088f0008 by task syz.0.1936/4656
> Call Trace:
>  ...
>  ocfs2_check_dir_entry.isra.0+0x31f/0x370 fs/ocfs2/dir.c:305
>  ocfs2_dir_foreach_blk_id+0x203/0xa70 fs/ocfs2/dir.c:1805
>  ocfs2_dir_foreach_blk fs/ocfs2/dir.c:1933 [inline]
>  ocfs2_readdir+0x4ba/0x520 fs/ocfs2/dir.c:1977
>  wrap_directory_iterator+0x9c/0xe0 fs/readdir.c:65
>  shared_ocfs2_readdir+0x29/0x40 fs/ocfs2/file.c:2822
>  iterate_dir+0x276/0x9e0 fs/readdir.c:108
>  __do_sys_getdents64 fs/readdir.c:410 [inline]
>  __se_sys_getdents64 fs/readdir.c:396 [inline]
>  __x64_sys_getdents64+0x143/0x2a0 fs/readdir.c:396
>  ...
> 
> [CAUSE]
> ocfs2_dir_foreach_blk_id() uses i_size_read(inode) as the loop bound
> after reading the inode block. Inline directories are only valid while
> i_size <= le16_to_cpu(data->id_count), but that invariant is never
> checked on read. Once ctx->pos reaches id_count, data->id_data +
> ctx->pos points past the inode block and can land in a freed neighbor
> page.
> 

ocfs2_read_inode_block() has already validated dinode->i_size.
So how it happens for the corrupted in-memory i_size?

Thanks,
Joseph

> [FIX]
> Validate i_size_read(inode) against data->id_count immediately after
> ocfs2_read_inode_block(). If the inline directory size exceeds its
> on-disk capacity, return -EFSCORRUPTED before constructing any dirent
> pointer. Keep the change local to ocfs2_dir_foreach_blk_id() so the
> patch stays scoped to the readdir bug.
> 
> Fixes: 23193e513d1c ("ocfs2: Read support for directories with inline data")
> Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
> ---
>  fs/ocfs2/dir.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
> index 8c9c4825f984..fa537505d1a9 100644
> --- a/fs/ocfs2/dir.c
> +++ b/fs/ocfs2/dir.c
> @@ -1761,6 +1761,7 @@ static int ocfs2_dir_foreach_blk_id(struct inode *inode,
>  				    struct dir_context *ctx)
>  {
>  	int ret, i;
> +	int error = 0;
>  	unsigned long offset = ctx->pos;
>  	struct buffer_head *di_bh = NULL;
>  	struct ocfs2_dinode *di;
> @@ -1777,6 +1778,12 @@ static int ocfs2_dir_foreach_blk_id(struct inode *inode,
>  	di = (struct ocfs2_dinode *)di_bh->b_data;
>  	data = &di->id2.i_data;
>  
> +	if (unlikely(i_size_read(inode) > le16_to_cpu(data->id_count))) {
> +		error = -EFSCORRUPTED;
> +		mlog_errno(error);
> +		goto out;
> +	}
> +
>  	while (ctx->pos < i_size_read(inode)) {
>  		/* If the dir block has changed since the last call to
>  		 * readdir(2), then we might be pointing to an invalid
> @@ -1819,7 +1826,7 @@ static int ocfs2_dir_foreach_blk_id(struct inode *inode,
>  	}
>  out:
>  	brelse(di_bh);
> -	return 0;
> +	return error;
>  }
>  
>  /*