Subject: [PATCH 4.16 179/279] bpf: fix possible spectre-v1 in find_and_alloc_map()

From: Greg Kroah-Hartman <[email-masked]>
Date: Mon, 18 Jun 2018 10:12:44 +0200

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Rutland <[email-masked]>

[ Upstream commit 9ef09e35e521bf0df5325cc9cffa726a8f5f3c1b ]

It's possible for userspace to control attr->map_type. Sanitize it when
using it as an array index to prevent an out-of-bounds value being used
under speculation.

Found by smatch.

Signed-off-by: Mark Rutland <[email-masked]>
Cc: Alexei Starovoitov <[email-masked]>
Cc: Dan Carpenter <[email-masked]>
Cc: Daniel Borkmann <[email-masked]>
Cc: Peter Zijlstra <[email-masked]>
Cc: [email-masked]
Acked-by: David S. Miller <[email-masked]>
Signed-off-by: Daniel Borkmann <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>
---
 kernel/bpf/syscall.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -26,6 +26,7 @@
 #include <linux/cred.h>
 #include <linux/timekeeping.h>
 #include <linux/ctype.h>
+#include <linux/nospec.h>
 
 #define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PROG_ARRAY || \
 			   (map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
@@ -102,12 +103,14 @@ const struct bpf_map_ops bpf_map_offload
 static struct bpf_map *find_and_alloc_map(union bpf_attr *attr)
 {
 	const struct bpf_map_ops *ops;
+	u32 type = attr->map_type;
 	struct bpf_map *map;
 	int err;
 
-	if (attr->map_type >= ARRAY_SIZE(bpf_map_types))
+	if (type >= ARRAY_SIZE(bpf_map_types))
 		return ERR_PTR(-EINVAL);
-	ops = bpf_map_types[attr->map_type];
+	type = array_index_nospec(type, ARRAY_SIZE(bpf_map_types));
+	ops = bpf_map_types[type];
 	if (!ops)
 		return ERR_PTR(-EINVAL);
 
@@ -122,7 +125,7 @@ static struct bpf_map *find_and_alloc_ma
 	if (IS_ERR(map))
 		return map;
 	map->ops = ops;
-	map->map_type = attr->map_type;
+	map->map_type = type;
 	return map;
 }