bpf: fix sk_skb programs without skb->dev assigned

Multiple BPF helpers in use by sk_skb programs calculate the max
skb length using the __bpf_skb_max_len function. However, this
calculates the max length using the skb->dev pointer which can be
NULL when an sk_skb program is paired with an sk_msg program.

To force this a sk_msg program needs to redirect into the ingress
path of a sock with an attach sk_skb program. Then the the sk_skb
program would need to call one of the helpers that adjust the skb
size.

To fix the null ptr dereference use SKB_MAX_ALLOC size if no dev
is available.

Fixes: 8934ce2fd081 ("bpf: sockmap redirect ingress support")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/net/core/filter.c b/net/core/filter.c
index 0ca6907d7efee75b68450f66c2c5a7172272895e..3095f1ba7015f560cccf96c45642490b20c96cc1 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2779,7 +2779,8 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 len_diff)
 
 static u32 __bpf_skb_max_len(const struct sk_buff *skb)
 {
-       return skb->dev->mtu + skb->dev->hard_header_len;
+       return skb->dev ? skb->dev->mtu + skb->dev->hard_header_len :
+                         SKB_MAX_ALLOC;
 }
 
 static int bpf_skb_adjust_net(struct sk_buff *skb, s32 len_diff)