[PATCH 6.18.y 3/3] ocfs2: fix out-of-bounds write in ocfs2_write_end_inline

[Sasha Levin <sashal@kernel.org>]

From: Joseph Qi <joseph.qi@linux.alibaba.com>

[ Upstream commit 7bc5da4842bed3252d26e742213741a4d0ac1b14 ]

KASAN reports a use-after-free write of 4086 bytes in
ocfs2_write_end_inline, called from ocfs2_write_end_nolock during a
copy_file_range splice fallback on a corrupted ocfs2 filesystem mounted on
a loop device.  The actual bug is an out-of-bounds write past the inode
block buffer, not a true use-after-free.  The write overflows into an
adjacent freed page, which KASAN reports as UAF.

The root cause is that ocfs2_try_to_write_inline_data trusts the on-disk
id_count field to determine whether a write fits in inline data.  On a
corrupted filesystem, id_count can exceed the physical maximum inline data
capacity, causing writes to overflow the inode block buffer.

Call trace (crash path):

   vfs_copy_file_range (fs/read_write.c:1634)
     do_splice_direct
       splice_direct_to_actor
         iter_file_splice_write
           ocfs2_file_write_iter
             generic_perform_write
               ocfs2_write_end
                 ocfs2_write_end_nolock (fs/ocfs2/aops.c:1949)
                   ocfs2_write_end_inline (fs/ocfs2/aops.c:1915)
                     memcpy_from_folio     <-- KASAN: write OOB

So add id_count upper bound check in ocfs2_validate_inode_block() to
alongside the existing i_size check to fix it.

Link: https://lkml.kernel.org/r/20260403063830.3662739-1-joseph.qi@linux.alibaba.com
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reported-by: syzbot+62c1793956716ea8b28a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=62c1793956716ea8b28a
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ocfs2/inode.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index e7d130f024f91..a840dde611c01 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1516,6 +1516,16 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 			goto bail;
 		}
 
+		if (le16_to_cpu(data->id_count) >
+		    ocfs2_max_inline_data_with_xattr(sb, di)) {
+			rc = ocfs2_error(sb,
+					 "Invalid dinode #%llu: inline data id_count %u exceeds max %d\n",
+					 (unsigned long long)bh->b_blocknr,
+					 le16_to_cpu(data->id_count),
+					 ocfs2_max_inline_data_with_xattr(sb, di));
+			goto bail;
+		}
+
 		if (le64_to_cpu(di->i_size) > le16_to_cpu(data->id_count)) {
 			rc = ocfs2_error(sb,
 					 "Invalid dinode #%llu: inline data i_size %llu exceeds id_count %u\n",
-- 
2.53.0