[PATCH bpf-next] bpf: fix sock_map_alloc() error path

[Eric Dumazet <eric.dumazet@gmail.com>]

From: Eric Dumazet <edumazet@google.com>

In case user program provides silly parameters, we want
a map_alloc() handler to return an error, not a NULL pointer,
otherwise we crash later in find_and_alloc_map()

Fixes: 174a79ff9515 ("bpf: sockmap with sk redirect support")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
---
 kernel/bpf/sockmap.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index 48c33417d13c0ad40154f25aeade0c9b4cafd96a..a927e89dad6e9591066c3a87afc497a196ebd887 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -521,8 +521,8 @@ static struct smap_psock *smap_init_psock(struct sock *sock,
 static struct bpf_map *sock_map_alloc(union bpf_attr *attr)
 {
 	struct bpf_stab *stab;
-	int err = -EINVAL;
 	u64 cost;
+	int err;
 
 	if (!capable(CAP_NET_ADMIN))
 		return ERR_PTR(-EPERM);
@@ -547,6 +547,7 @@ static struct bpf_map *sock_map_alloc(union bpf_attr *attr)
 
 	/* make sure page count doesn't overflow */
 	cost = (u64) stab->map.max_entries * sizeof(struct sock *);
+	err = -EINVAL;
 	if (cost >= U32_MAX - PAGE_SIZE)
 		goto free_stab;