[PATCH] ocfs2: Avoid NULL pointer dereference in dx_dir_lookup_rec()

[Ivan Pravdin <ipravdin.official@gmail.com>]

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 for a NULL 'rec' and use an alternate error
message in that case to avoid unsafe access.

Reported-by: syzbot+20282c1b2184a857ac4c@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/67483b75.050a0220.253251.007c.GAE@google.com/T/
Signed-off-by: Ivan Pravdin <ipravdin.official@gmail.com>
---
 fs/ocfs2/dir.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
index 7799f4d16ce9..dccf0349e523 100644
--- a/fs/ocfs2/dir.c
+++ b/fs/ocfs2/dir.c
@@ -809,11 +809,17 @@ static int ocfs2_dx_dir_lookup_rec(struct inode *inode,
 	}
 
 	if (!found) {
-		ret = ocfs2_error(inode->i_sb,
-				  "Inode %lu has bad extent record (%u, %u, 0) in btree\n",
-				  inode->i_ino,
-				  le32_to_cpu(rec->e_cpos),
-				  ocfs2_rec_clusters(el, rec));
+		if (rec) {
+			ret = ocfs2_error(inode->i_sb,
+					"Inode %lu has bad extent record (%u, %u, 0) in btree\n",
+					inode->i_ino,
+					le32_to_cpu(rec->e_cpos),
+					ocfs2_rec_clusters(el, rec));
+		} else {
+			ret = ocfs2_error(inode->i_sb,
+					"Inode %lu has no extent records in btree\n",
+					inode->i_ino);
+		}
 		goto out;
 	}
 
-- 
2.45.2