2020-11-11 20:49:33

by Alexander Lobakin

Subject: [PATCH v5 net 1/2] net: udp: fix UDP header access on Fast/frag0 UDP GRO

UDP GRO uses udp_hdr(skb) in its .gro_receive() callback. While it's
probably OK for non-frag0 paths (when all headers or even the entire
frame are already in skb head), this inline points to junk when
using Fast GRO (napi_gro_frags() or napi_gro_receive() with only
Ethernet header in skb head and all the rest in the frags) and breaks
GRO packet compilation and the packet flow itself.
To support both modes, skb_gro_header_fast() + skb_gro_header_slow()
are typically used. UDP even has an inline helper that makes use of
them, udp_gro_udphdr(). Use that instead of troublemaking udp_hdr()
to get rid of the out-of-order delivers.

Present since the introduction of plain UDP GRO in 5.0-rc1.

Fixes: e20cf8d3f1f7 ("udp: implement GRO for plain UDP sockets.")
Cc: Eric Dumazet <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Signed-off-by: Alexander Lobakin <[email protected]>
---
net/ipv4/udp_offload.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index e67a66fbf27b..13740e9fe6ec 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -366,7 +366,7 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
struct sk_buff *skb)
{
- struct udphdr *uh = udp_hdr(skb);
+ struct udphdr *uh = udp_gro_udphdr(skb);
struct sk_buff *pp = NULL;
struct udphdr *uh2;
struct sk_buff *p;
--
2.29.2

2020-11-11 20:55:43

by Willem de Bruijn

Subject: Re: [PATCH v5 net 1/2] net: udp: fix UDP header access on Fast/frag0 UDP GRO

On Wed, Nov 11, 2020 at 3:45 PM Alexander Lobakin <[email protected]> wrote:
>
> UDP GRO uses udp_hdr(skb) in its .gro_receive() callback. While it's
> probably OK for non-frag0 paths (when all headers or even the entire
> frame are already in skb head), this inline points to junk when
> using Fast GRO (napi_gro_frags() or napi_gro_receive() with only
> Ethernet header in skb head and all the rest in the frags) and breaks
> GRO packet compilation and the packet flow itself.
> To support both modes, skb_gro_header_fast() + skb_gro_header_slow()
> are typically used. UDP even has an inline helper that makes use of
> them, udp_gro_udphdr(). Use that instead of troublemaking udp_hdr()
> to get rid of the out-of-order delivers.
>
> Present since the introduction of plain UDP GRO in 5.0-rc1.
>
> Fixes: e20cf8d3f1f7 ("udp: implement GRO for plain UDP sockets.")
> Cc: Eric Dumazet <[email protected]>
> Cc: Jakub Kicinski <[email protected]>
> Cc: Willem de Bruijn <[email protected]>
> Signed-off-by: Alexander Lobakin <[email protected]>

Acked-by: Willem de Bruijn <[email protected]>