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net/flow_dissector: correctly cap nhoff and thoff in case of BPF 

We want to make sure that the following condition holds:
0 <= nhoff <= thoff <= skb->len

BPF program can set out-of-bounds nhoff and thoff, which is dangerous, see
recent commit d0c081b491 ("flow_dissector: properly cap thoff field")'.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Stanislav Fomichev 2018-12-05 20:40:48 -08:00 committed by Alexei Starovoitov
parent 13e56ec2cc
commit ec3d837aac
1 changed files with 4 additions and 1 deletions
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5
net/core/flow_dissector.c
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@ -791,9 +791,12 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
/* Restore state */
memcpy(cb, &cb_saved, sizeof(cb_saved));
flow_keys.nhoff = clamp_t(u16, flow_keys.nhoff, 0, skb->len);
flow_keys.thoff = clamp_t(u16, flow_keys.thoff,
flow_keys.nhoff, skb->len);
__skb_flow_bpf_to_target(&flow_keys, flow_dissector,
target_container);
key_control->thoff = min_t(u16, key_control->thoff, skb->len);
rcu_read_unlock();
return result == BPF_OK;
}