[PATCH] ext4: Verify extent header in ext4_find_extent()

[Shigeru Yoshida]

syzbot reported use-after-free in ext4_find_extent() [1].  If there is
a corrupted file system, this can cause invalid memory access.

This patch fixes the issue by verifying extent header.

Reported-by: syzbot+bf4bb7731ef73b83a3b4@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://syzkaller.appspot.com/bug?id=cd95cb722bfa1234ac4c78345c8953ee2e7170d0 [1]
Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
---
 fs/ext4/extents.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 9de1c9d1a13d..79bfa583ab1d 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -901,6 +901,9 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block,
 		ret = -EFSCORRUPTED;
 		goto err;
 	}
+	ret = ext4_ext_check(inode, eh, depth, 0);
+	if (ret)
+		goto err;
 
 	if (path) {
 		ext4_ext_drop_refs(path);
-- 
2.38.1