4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jan Kara <jack@xxxxxxx>
[ Upstream commit 65121eff3e4c8c90f8126debf3c369228691c591 ]
If the extended attribute size is not a multiple of block size, the last
block in the EA inode will have uninitialized tail which will get
written to disk. We will never expose the data to userspace but still
this is not a good practice so just zero out the tail of the block as it
isn't going to cause a noticeable performance overhead.
Fixes: e50e5129f384 ("ext4: xattr-in-inode support")
Reported-by: syzbot+9c1fe13fcb51574b249b@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Link: https://patch.msgid.link/20240613150234.25176-1-jack@xxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/ext4/xattr.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index dc42a8fba0d22..e9299f769dbfe 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1420,6 +1420,12 @@ static int ext4_xattr_inode_write(handle_t *handle, struct inode *ea_inode,
goto out;
memcpy(bh->b_data, buf, csize);
+ /*
+ * Zero out block tail to avoid writing uninitialized memory
+ * to disk.
+ */
+ if (csize < blocksize)
+ memset(bh->b_data + csize, 0, blocksize - csize);
set_buffer_uptodate(bh);
ext4_handle_dirty_metadata(handle, ea_inode, bh);
--
2.43.0
