ubifs: Check data node size before truncate

commit 95a22d20 upstream.

Check whether the size is within bounds before using it.
If the size is not correct, abort and dump the bad data node.

Cc: Kees Cook <keescook@chromium.org>
Cc: Silvio Cesare <silvio.cesare@gmail.com>
Cc: stable@vger.kernel.org
Fixes: 1e51764a ("UBIFS: add new flash file system")
Reported-by: Silvio Cesare <silvio.cesare@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/ubifs/journal.c

@@ -1186,7 +1186,16 @@ int ubifs_jnl_truncate(struct ubifs_info *c, const struct inode *inode,
 		else if (err)
 			goto out_free;
 		else {
-			if (le32_to_cpu(dn->size) <= dlen)
+			int dn_len = le32_to_cpu(dn->size);
+
+			if (dn_len <= 0 || dn_len > UBIFS_BLOCK_SIZE) {
+				ubifs_err(c, "bad data node (block %u, inode %lu)",
+					  blk, inode->i_ino);
+				ubifs_dump_node(c, dn);
+				goto out_free;
+			}
+
+			if (dn_len <= dlen)
 				dlen = 0; /* Nothing to do */
 			else {
 				int compr_type = le16_to_cpu(dn->compr_type);