[PATCH] ntfs: add check for mft record size in superblock

[Rustam Kovhaev]

number of bytes allocated for mft record should be equal to the mft
record size stored in ntfs superblock
as reported by syzbot, userspace might trigger out-of-bounds read by
dereferencing ctx->attr in ntfs_attr_find()

Reported-and-tested-by: syzbot+aed06913f36eff9b544e@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://syzkaller.appspot.com/bug?extid=aed06913f36eff9b544e
Signed-off-by: Rustam Kovhaev <rkovhaev@xxxxxxxxx>
Acked-by: Anton Altaparmakov <anton@xxxxxxxxxx>
---
 fs/ntfs/inode.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
index 9bb9f0952b18..caf563981532 100644
--- a/fs/ntfs/inode.c
+++ b/fs/ntfs/inode.c
@@ -1810,6 +1810,12 @@ int ntfs_read_inode_mount(struct inode *vi)
 		brelse(bh);
 	}
 
+	if (le32_to_cpu(m->bytes_allocated) != vol->mft_record_size) {
+		ntfs_error(sb, "Incorrect mft record size %u in superblock, should be %u.",
+				le32_to_cpu(m->bytes_allocated), vol->mft_record_size);
+		goto err_out;
+	}
+
 	/* Apply the mst fixups. */
 	if (post_read_mst_fixup((NTFS_RECORD*)m, vol->mft_record_size)) {
 		/* FIXME: Try to use the $MFTMirr now. */
-- 
2.28.0