[PATCH v2 net] gso: fix dodgy bit handling for GSO_UDP_L4

[PATCH v2 net] gso: fix dodgy bit handling for GSO_UDP_L4

[Yan Zhai]

Commit 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4
packets.") checks DODGY bit for UDP, but for packets that can be fed
directly to the device after gso_segs reset, it actually falls through
to fragmentation:

https://lore.kernel.org/all/CAJPywTKDdjtwkLVUW6LRA2FU912qcDmQOQGt2WaDo28KzYDg+A@mail.gmail.com/

This change restores the expected behavior of GSO_UDP_L4 packets.

Fixes: 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4 packets.")
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Signed-off-by: Yan Zhai <yan@cloudflare.com>

---
v2: dropped modifications to tcp/sctp on DODGY bit removal after
validating gso_segs. Also moved the UDP header check into
__udp_gso_segment (per Willem's suggestion).

---
 net/ipv4/udp_offload.c | 16 +++++++++++-----
 net/ipv6/udp_offload.c |  3 +--
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 75aa4de5b731..f402946da344 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -274,13 +274,20 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 	__sum16 check;
 	__be16 newlen;
 
-	if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST)
-		return __udp_gso_segment_list(gso_skb, features, is_ipv6);
-
 	mss = skb_shinfo(gso_skb)->gso_size;
 	if (gso_skb->len <= sizeof(*uh) + mss)
 		return ERR_PTR(-EINVAL);
 
+	if (skb_gso_ok(gso_skb, features | NETIF_F_GSO_ROBUST)) {
+		/* Packet is from an untrusted source, reset gso_segs. */
+		skb_shinfo(gso_skb)->gso_segs = DIV_ROUND_UP(gso_skb->len - sizeof(*uh),
+							     mss);
+		return NULL;
+	}
+
+	if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST)
+		return __udp_gso_segment_list(gso_skb, features, is_ipv6);
+
 	skb_pull(gso_skb, sizeof(*uh));
 
 	/* clear destructor to avoid skb_segment assigning it to tail */
@@ -388,8 +395,7 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 		goto out;
 
-	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4 &&
-	    !skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST))
+	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
 		return __udp_gso_segment(skb, features, false);
 
 	mss = skb_shinfo(skb)->gso_size;
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index ad3b8726873e..09fa7a42cb93 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -43,8 +43,7 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 		if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 			goto out;
 
-		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4 &&
-		    !skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST))
+		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
 			return __udp_gso_segment(skb, features, true);
 
 		mss = skb_shinfo(skb)->gso_size;
-- 
2.30.2

Re: [PATCH v2 net] gso: fix dodgy bit handling for GSO_UDP_L4

[Willem de Bruijn]

On Thu, Jul 13, 2023 at 1:28 PM Yan Zhai <yan@cloudflare.com> wrote:
>
> Commit 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4
> packets.") checks DODGY bit for UDP, but for packets that can be fed
> directly to the device after gso_segs reset, it actually falls through
> to fragmentation:
>
> https://lore.kernel.org/all/CAJPywTKDdjtwkLVUW6LRA2FU912qcDmQOQGt2WaDo28KzYDg+A@mail.gmail.com/
>
> This change restores the expected behavior of GSO_UDP_L4 packets.
>
> Fixes: 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4 packets.")
> Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
> Signed-off-by: Yan Zhai <yan@cloudflare.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>

for next time: places hyperlinks in the block of tags at the bottom of
the commit as "Link: ${URL}"

Re: [PATCH v2 net] gso: fix dodgy bit handling for GSO_UDP_L4

[Jason Wang]

On Fri, Jul 14, 2023 at 1:28 AM Yan Zhai <yan@cloudflare.com> wrote:
>
> Commit 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4
> packets.") checks DODGY bit for UDP, but for packets that can be fed
> directly to the device after gso_segs reset, it actually falls through
> to fragmentation:
>
> https://lore.kernel.org/all/CAJPywTKDdjtwkLVUW6LRA2FU912qcDmQOQGt2WaDo28KzYDg+A@mail.gmail.com/
>
> This change restores the expected behavior of GSO_UDP_L4 packets.
>
> Fixes: 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4 packets.")
> Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
> Signed-off-by: Yan Zhai <yan@cloudflare.com>
>
> ---
> v2: dropped modifications to tcp/sctp on DODGY bit removal after
> validating gso_segs. Also moved the UDP header check into
> __udp_gso_segment (per Willem's suggestion).
>

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks

Re: [PATCH v2 net] gso: fix dodgy bit handling for GSO_UDP_L4

[Yan Zhai]

On Thu, Jul 13, 2023 at 12:38 PM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> On Thu, Jul 13, 2023 at 1:28 PM Yan Zhai <yan@cloudflare.com> wrote:
> >
> > Commit 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4
> > packets.") checks DODGY bit for UDP, but for packets that can be fed
> > directly to the device after gso_segs reset, it actually falls through
> > to fragmentation:
> >
> > https://lore.kernel.org/all/CAJPywTKDdjtwkLVUW6LRA2FU912qcDmQOQGt2WaDo28KzYDg+A@mail.gmail.com/
> >
> > This change restores the expected behavior of GSO_UDP_L4 packets.
> >
> > Fixes: 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4 packets.")
> > Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
> > Signed-off-by: Yan Zhai <yan@cloudflare.com>
>
> Reviewed-by: Willem de Bruijn <willemb@google.com>
>
> for next time: places hyperlinks in the block of tags at the bottom of
> the commit as "Link: ${URL}"

Good to learn, thanks!
--
Yan

Re: [PATCH v2 net] gso: fix dodgy bit handling for GSO_UDP_L4

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by David S. Miller <davem@davemloft.net>:

On Thu, 13 Jul 2023 10:28:00 -0700 you wrote:
> Commit 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4
> packets.") checks DODGY bit for UDP, but for packets that can be fed
> directly to the device after gso_segs reset, it actually falls through
> to fragmentation:
> 
> https://lore.kernel.org/all/CAJPywTKDdjtwkLVUW6LRA2FU912qcDmQOQGt2WaDo28KzYDg+A@mail.gmail.com/
> 
> [...]

Here is the summary with links:
  - [v2,net] gso: fix dodgy bit handling for GSO_UDP_L4
    https://git.kernel.org/netdev/net/c/9840036786d9

You are awesome, thank you!
-- 
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