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ext4: Avoid writing unitialized memory to disk in EA inodes

Message ID 20240613150234.25176-1-jack@suse.cz
State New
Headers show
Series ext4: Avoid writing unitialized memory to disk in EA inodes | expand

Commit Message

Jan Kara June 13, 2024, 3:02 p.m. UTC 
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@syzkaller.appspotmail.com
Reported-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/xattr.c | 6 ++++++
 1 file changed, 6 insertions(+)
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Patch

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 6460879b9fcb..46ce2f21fef9 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1433,6 +1433,12 @@  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);