When a directory entry is not found, ocfs2_dx_dir_lookup_rec() prints an
error message that unconditionally dereferences the 'rec' pointer.
However, if 'rec' is NULL, this leads to a NULL pointer dereference and
a kernel panic.

Add an explicit check empty extent list to avoid dereferencing NULL
'rec' pointer.

Reported-by: syzbot+20282c1b2184a857ac4c@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/67cd7e29.050a0220.e1a89.0007.GAE@google.com/
Signed-off-by: Ivan Pravdin <ipravdin.official@gmail.com>
---
v1 -> v2: Changed 'Closes:' tag to point to the correct bug report.
v2 -> v3: Added an explicit check for empty extent list before dereferencing 'rec'.

 fs/ocfs2/dir.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
index 7799f4d16ce9..acbae902ae3a 100644
--- a/fs/ocfs2/dir.c
+++ b/fs/ocfs2/dir.c
@@ -798,6 +798,14 @@ static int ocfs2_dx_dir_lookup_rec(struct inode *inode,
 		}
 	}
 
+	if (le16_to_cpu(el->l_next_free_rec) == 0) {
+		ret = ocfs2_error(inode->i_sb,
+				  "Inode %lu has empty extent list at depth %u\n",
+				  inode->i_ino, 
+				  le16_to_cpu(el->l_tree_depth));
+		goto out;
+	}
+
 	found = 0;
 	for (i = le16_to_cpu(el->l_next_free_rec) - 1; i >= 0; i--) {
 		rec = &el->l_recs[i];
-- 
2.45.2

On 2025/7/8 08:10, Ivan Pravdin wrote:
> When a directory entry is not found, ocfs2_dx_dir_lookup_rec() prints an
> error message that unconditionally dereferences the 'rec' pointer.
> However, if 'rec' is NULL, this leads to a NULL pointer dereference and
> a kernel panic.
> 
> Add an explicit check empty extent list to avoid dereferencing NULL
> 'rec' pointer.
> 
> Reported-by: syzbot+20282c1b2184a857ac4c@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/67cd7e29.050a0220.e1a89.0007.GAE@google.com/
> Signed-off-by: Ivan Pravdin <ipravdin.official@gmail.com>

Looks fine.

Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
> ---
> v1 -> v2: Changed 'Closes:' tag to point to the correct bug report.
> v2 -> v3: Added an explicit check for empty extent list before dereferencing 'rec'.
> 
>  fs/ocfs2/dir.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
> index 7799f4d16ce9..acbae902ae3a 100644
> --- a/fs/ocfs2/dir.c
> +++ b/fs/ocfs2/dir.c
> @@ -798,6 +798,14 @@ static int ocfs2_dx_dir_lookup_rec(struct inode *inode,
>  		}
>  	}
>  
> +	if (le16_to_cpu(el->l_next_free_rec) == 0) {
> +		ret = ocfs2_error(inode->i_sb,
> +				  "Inode %lu has empty extent list at depth %u\n",
> +				  inode->i_ino, 
> +				  le16_to_cpu(el->l_tree_depth));
> +		goto out;
> +	}
> +
>  	found = 0;
>  	for (i = le16_to_cpu(el->l_next_free_rec) - 1; i >= 0; i--) {
>  		rec = &el->l_recs[i];