Commit 0c6bc6e5 authored Jul 05, 2018 by John Fastabend Committed by Alexei Starovoitov Jul 07, 2018

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: 8934ce2f ("bpf: sockmap redirect ingress support")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

parent 631da853

net/core/filter.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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)

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