linux-kernel - [PATCH] ext4: validate xattr entries in ext4_xattr_move_to

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Message-ID: <20250923092512.1088241-1-kartikey406@gmail.com>
Date: Tue, 23 Sep 2025 14:55:12 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: tytso@....edu
Cc: adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Deepanshu Kartikey <kartikey406@...il.com>,
	syzbot+4c9d23743a2409b80293@...kaller.appspotmail.com
Subject: [PATCH] ext4: validate xattr entries in ext4_xattr_move_to_block

During inode expansion, ext4_xattr_move_to_block() processes xattr entries
from on-disk structures without validating their integrity. Corrupted
filesystems may contain xattr entries where e_value_size is zero but
e_value_inum is non-zero, indicating the entry claims to store its value
in a separate inode but has no actual value.

This corruption pattern leads to a WARNING in ext4_xattr_block_set() when
it encounters i->value_len of zero while i->in_inode is set, violating
the function's invariant that in-inode xattrs must have non-zero length.

Add validation in ext4_xattr_move_to_block() to detect this specific
corruption pattern and return -EFSCORRUPTED, preventing the invalid
data from propagating to downstream functions and causing warnings.

Reported-by: syzbot+4c9d23743a2409b80293@...kaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=4c9d23743a2409b80293
Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
---
 fs/ext4/xattr.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 5a6fe1513fd2..60e224c622b4 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -2607,7 +2607,10 @@ static int ext4_xattr_move_to_block(handle_t *handle, struct inode *inode,
 	struct ext4_xattr_ibody_header *header = IHDR(inode, raw_inode);
 	int needs_kvfree = 0;
 	int error;
-
+	if (value_size == 0 && entry->e_value_inum != 0) {
+		error = -EFSCORRUPTED;
+		goto out;
+	}
 	is = kzalloc(sizeof(struct ext4_xattr_ibody_find), GFP_NOFS);
 	bs = kzalloc(sizeof(struct ext4_xattr_block_find), GFP_NOFS);
 	b_entry_name = kmalloc(entry->e_name_len + 1, GFP_NOFS);
-- 
2.43.0