netdev - [PATCH bpf 3/5] flow_dissector: fix clamping of BPF flow

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Message-Id: <20190401205734.4400-4-sdf@google.com>
Date:   Mon,  1 Apr 2019 13:57:32 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     netdev@...r.kernel.org, bpf@...r.kernel.org
Cc:     davem@...emloft.net, ast@...nel.org, daniel@...earbox.net,
        simon.horman@...ronome.com, willemb@...gle.com,
        peterpenkov96@...il.com, Stanislav Fomichev <sdf@...gle.com>
Subject: [PATCH bpf 3/5] flow_dissector: fix clamping of BPF flow_keys for
 non-zero nhoff

Don't allow BPF program to set flow_keys->nhoff to less than initial
value. We currently don't read the value afterwards in anything but
the tests, but it's still a good practice to return consistent
values to the test programs.

Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
---
 net/core/flow_dissector.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 9b84250039df..94a450b2191a 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -717,7 +717,8 @@ bool __skb_flow_bpf_dissect(struct bpf_prog *prog,
 	/* Restore state */
 	memcpy(cb, &cb_saved, sizeof(cb_saved));
 
-	flow_keys->nhoff = clamp_t(u16, flow_keys->nhoff, 0, skb->len);
+	flow_keys->nhoff = clamp_t(u16, flow_keys->nhoff,
+				   skb_network_offset(skb), skb->len);
 	flow_keys->thoff = clamp_t(u16, flow_keys->thoff,
 				   flow_keys->nhoff, skb->len);
 
-- 
2.21.0.392.gf8f6787159e-goog