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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: 8934ce2fd0 ("bpf: sockmap redirect ingress support")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
John Fastabend 2018-07-05 08:49:59 -07:00 committed by Alexei Starovoitov
parent 631da8534a
commit 0c6bc6e531
1 changed files with 2 additions and 1 deletions
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3
net/core/filter.c
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@ -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)