Forwarded: [PATCH] ext4: fix use-after-free in ext4_search_dir via corrupted inline xattr

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Subject: [PATCH] ext4: fix use-after-free in ext4_search_dir via corrupted inline xattr
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Add bounds validation for inline directory xattr data to prevent
use-after-free when accessing corrupted filesystems.

ext4_find_inline_entry() performs two directory searches: first in
the i_block area, then in the extended attribute (xattr) area of the
inode. When calculating inline_start for the xattr area via
ext4_get_inline_xattr_pos(), the function trusts the e_value_offs
field from disk without validating the resulting pointer stays within
the inode's boundaries.

A corrupted filesystem can craft a malicious e_value_offs value that
causes inline_start to point outside the inode's allocated space,
potentially into freed memory. When ext4_search_dir() attempts to
access this invalid pointer, it results in a KASAN use-after-free.

Fix this by validating that inline_start and inline_start + inline_size
remain within the inode's boundaries before calling ext4_search_dir().
Return -EFSCORRUPTED if the bounds check fails.

Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/ext4/inline.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 1b094a4f3866..28ac90a8d5a2 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1617,7 +1617,15 @@ struct buffer_head *ext4_find_inline_entry(struct inode *dir,
 
 	inline_start = ext4_get_inline_xattr_pos(dir, &is.iloc);
 	inline_size = ext4_get_inline_size(dir) - EXT4_MIN_INLINE_DATA_SIZE;
-
+	void *inode_start = ext4_raw_inode(&is.iloc);
+	void *inode_end = inode_start + EXT4_INODE_SIZE(dir->i_sb);
+
+	if (inline_start < inode_start ||
+	    inline_start >= inode_end ||
+	    inline_start + inline_size > inode_end) {
+		ret = -EFSCORRUPTED;
+		goto out;
+	}
 	ret = ext4_search_dir(is.iloc.bh, inline_start, inline_size,
 			      dir, fname, 0, res_dir);
 	if (ret == 1)
-- 
2.43.0