ntfs3: fix uninit memory after failed mi_read in mi_format_new

Fix a KMSAN un-init bug found by syzkaller.

ntfs_get_bh() expects a buffer from sb_getblk(), that buffer may not be
uptodate. We do not bring the buffer uptodate before setting it as
uptodate. If the buffer were to not be uptodate, it could mean adding a
buffer with un-init data to the mi record. Attempting to load that record
will trigger KMSAN.

Avoid this by setting the buffer as uptodate, if it’s not already, by
overwriting it.

Reported-by: syzbot+7a2ba6b7b66340cff225@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7a2ba6b7b66340cff225
Tested-by: syzbot+7a2ba6b7b66340cff225@syzkaller.appspotmail.com
Fixes: 4342306 ("fs/ntfs3: Add file operations and implementation")
Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

Author: rpthibeault

fs/ntfs3/fsntfs.c

@@ -1349,7 +1349,14 @@ int ntfs_get_bh(struct ntfs_sb_info *sbi, const struct runs_tree *run, u64 vbo,
 				}
 				if (buffer_locked(bh))
 					__wait_on_buffer(bh);
-				set_buffer_uptodate(bh);
+
+				lock_buffer(bh);
+				if (!buffer_uptodate(bh))
+				{
+					memset(bh->b_data, 0, blocksize);
+					set_buffer_uptodate(bh);
+				}
+				unlock_buffer(bh);
 			} else {
 				bh = ntfs_bread(sb, block);
 				if (!bh) {