Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf

Alexei Starovoitov says:

====================
pull-request: bpf 2018-02-02

The following pull-request contains BPF updates for your *net* tree.

The main changes are:

1) support XDP attach in libbpf, from Eric.

2) minor fixes, from Daniel, Jakub, Yonghong, Alexei.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/core.c

@@ -1576,25 +1576,41 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
 				__u32 __user *prog_ids, u32 cnt)
 {
 	struct bpf_prog **prog;
-	u32 i = 0, id;
+	unsigned long err = 0;
+	u32 i = 0, *ids;
+	bool nospc;
 
+	/* users of this function are doing:
+	 * cnt = bpf_prog_array_length();
+	 * if (cnt > 0)
+	 *     bpf_prog_array_copy_to_user(..., cnt);
+	 * so below kcalloc doesn't need extra cnt > 0 check, but
+	 * bpf_prog_array_length() releases rcu lock and
+	 * prog array could have been swapped with empty or larger array,
+	 * so always copy 'cnt' prog_ids to the user.
+	 * In a rare race the user will see zero prog_ids
+	 */
+	ids = kcalloc(cnt, sizeof(u32), GFP_USER);
+	if (!ids)
+		return -ENOMEM;
 	rcu_read_lock();
 	prog = rcu_dereference(progs)->progs;
 	for (; *prog; prog++) {
 		if (*prog == &dummy_bpf_prog.prog)
 			continue;
-		id = (*prog)->aux->id;
-		if (copy_to_user(prog_ids + i, &id, sizeof(id))) {
-			rcu_read_unlock();
-			return -EFAULT;
-		}
+		ids[i] = (*prog)->aux->id;
 		if (++i == cnt) {
 			prog++;
 			break;
 		}
 	}
+	nospc = !!(*prog);
 	rcu_read_unlock();
-	if (*prog)
+	err = copy_to_user(prog_ids, ids, cnt * sizeof(u32));
+	kfree(ids);
+	if (err)
+		return -EFAULT;
+	if (nospc)
 		return -ENOSPC;
 	return 0;
 }