Re: [PATCH net] net: __skb_flow_dissect() must cap its return value

[David Miller]

From: Eric Dumazet 
Date: Wed, 09 Nov 2016 16:04:46 -0800

> From: Eric Dumazet 
> 
> After Tom patch, thoff field could point past the end of the buffer,
> this could fool some callers.
> 
> If an skb was provided, skb->len should be the upper limit.
> If not, hlen is supposed to be the upper limit.
> 
> Fixes: a6e544b0a88b ("flow_dissector: Jump to exit code in 
> __skb_flow_dissect")
> Signed-off-by: Eric Dumazet 
> Reported-by: Yibin Yang  Acked-by: Alexander Duyck 
> Acked-by: Willem de Bruijn 
> Acked-by: Alexei Starovoitov 

Applied and queued up for -stable, thanks Eric.

[PATCH net] net: __skb_flow_dissect() must cap its return value

[Eric Dumazet]

From: Eric Dumazet 

After Tom patch, thoff field could point past the end of the buffer,
this could fool some callers.

If an skb was provided, skb->len should be the upper limit.
If not, hlen is supposed to be the upper limit.

Fixes: a6e544b0a88b ("flow_dissector: Jump to exit code in __skb_flow_dissect")
Signed-off-by: Eric Dumazet 
Reported-by: Yibin Yang 
Acked-by: Willem de Bruijn 
Acked-by: Alexei Starovoitov 
---
 net/core/flow_dissector.c |   11 ---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 44e6ba9d3a6b..5a908c534bec 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -122,7 +122,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
struct flow_dissector_key_keyid *key_keyid;
bool skip_vlan = false;
u8 ip_proto = 0;
-   bool ret = false;
+   bool ret;
 
if (!data) {
data = skb->data;
@@ -549,12 +549,17 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 out_good:
ret = true;
 
-out_bad:
+   key_control->thoff = (u16)nhoff;
+out:
key_basic->n_proto = proto;
key_basic->ip_proto = ip_proto;
-   key_control->thoff = (u16)nhoff;
 
return ret;
+
+out_bad:
+   ret = false;
+   key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen);
+   goto out;
 }
 EXPORT_SYMBOL(__skb_flow_dissect);