[PATCH bpf] bpf: only test gso type on gso packets

[PATCH bpf] bpf: only test gso type on gso packets

[Willem de Bruijn]

From: Willem de Bruijn <willemb@google.com>

BPF can adjust gso only for tcp bytestreams. Fail on other gso types.

But only on gso packets. It does not touch this field if !gso_size.

Fixes: b90efd225874 ("bpf: only adjust gso_size on bytestream protocols")
Signed-off-by: Willem de Bruijn <willemb@google.com>

---

Stupid bug on my part. Found only when adding tests for the feature.
Will try to upstream those once bpf-next opens.

On a related note, also working on a flag BPF_F_ADJ_ROOM_FIXED_GSO
that will allow reenabling this field for UDP (and possibly avoiding
the expensive skb_cow for the TCP common case).
---
 include/linux/skbuff.h | 4 ++--
 net/core/filter.c      | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 27beb549ffbe1..f32f32407dc43 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4232,10 +4232,10 @@ static inline bool skb_is_gso_sctp(const struct sk_buff *skb)
 	return skb_shinfo(skb)->gso_type & SKB_GSO_SCTP;
 }
 
+/* Note: Should be called only if skb_is_gso(skb) is true */
 static inline bool skb_is_gso_tcp(const struct sk_buff *skb)
 {
-	return skb_is_gso(skb) &&
-	       skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6);
+	return skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6);
 }
 
 static inline void skb_gso_reset(struct sk_buff *skb)
diff --git a/net/core/filter.c b/net/core/filter.c
index 5ceba98069d46..f274620945ff0 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2804,7 +2804,7 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb)
 	u32 off = skb_mac_header_len(skb);
 	int ret;
 
-	if (!skb_is_gso_tcp(skb))
+	if (skb_is_gso(skb) && !skb_is_gso_tcp(skb))
 		return -ENOTSUPP;
 
 	ret = skb_cow(skb, len_diff);
@@ -2845,7 +2845,7 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb)
 	u32 off = skb_mac_header_len(skb);
 	int ret;
 
-	if (!skb_is_gso_tcp(skb))
+	if (skb_is_gso(skb) && !skb_is_gso_tcp(skb))
 		return -ENOTSUPP;
 
 	ret = skb_unclone(skb, GFP_ATOMIC);
@@ -2970,7 +2970,7 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 len_diff)
 	u32 off = skb_mac_header_len(skb) + bpf_skb_net_base_len(skb);
 	int ret;
 
-	if (!skb_is_gso_tcp(skb))
+	if (skb_is_gso(skb) && !skb_is_gso_tcp(skb))
 		return -ENOTSUPP;
 
 	ret = skb_cow(skb, len_diff);
@@ -2999,7 +2999,7 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 len_diff)
 	u32 off = skb_mac_header_len(skb) + bpf_skb_net_base_len(skb);
 	int ret;
 
-	if (!skb_is_gso_tcp(skb))
+	if (skb_is_gso(skb) && !skb_is_gso_tcp(skb))
 		return -ENOTSUPP;
 
 	ret = skb_unclone(skb, GFP_ATOMIC);
-- 
2.21.0.352.gf09ad66450-goog

Re: [PATCH bpf] bpf: only test gso type on gso packets

[Y Song]

On Wed, Mar 6, 2019 at 1:15 PM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> From: Willem de Bruijn <willemb@google.com>
>
> BPF can adjust gso only for tcp bytestreams. Fail on other gso types.
>
> But only on gso packets. It does not touch this field if !gso_size.
Could you specify which field you are referring here?
gso_type, gso_segs, gso_size?

>
> Fixes: b90efd225874 ("bpf: only adjust gso_size on bytestream protocols")
> Signed-off-by: Willem de Bruijn <willemb@google.com>

Other than the above commit message suggestion,
Acked-by: Yonghong Song <yhs@fb.com>

Re: [PATCH bpf] bpf: only test gso type on gso packets

[Daniel Borkmann]

On 03/06/2019 08:35 PM, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
> 
> BPF can adjust gso only for tcp bytestreams. Fail on other gso types.
> 
> But only on gso packets. It does not touch this field if !gso_size.
> 
> Fixes: b90efd225874 ("bpf: only adjust gso_size on bytestream protocols")
> Signed-off-by: Willem de Bruijn <willemb@google.com>

Good catch, applied, thanks!

> Stupid bug on my part. Found only when adding tests for the feature.
> Will try to upstream those once bpf-next opens.
> 
> On a related note, also working on a flag BPF_F_ADJ_ROOM_FIXED_GSO
> that will allow reenabling this field for UDP (and possibly avoiding
> the expensive skb_cow for the TCP common case).

Nice, looking forward!