Re: [PATCH net] gso: fix GSO_DODGY bit handling for related protocols
From: Jason Wang <hidden>
Date: 2023-07-13 02:12:06
Also in:
linux-sctp, lkml
On Thu, Jul 13, 2023 at 9:55 AM Yan Zhai [off-list ref] wrote:
SKB_GSO_DODGY bit indicates a GSO packet comes from an untrusted source.
The canonical way is to recompute the gso_segs to avoid device driver
issues. Afterwards, the DODGY bit can be removed to avoid re-check at the
egress of later devices, e.g. packets can egress to a vlan device backed
by a real NIC.
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 [1].
Commit 90017accff61 ("sctp: Add GSO support") and commit 3820c3f3e417
("[TCP]: Reset gso_segs if packet is dodgy") both didn't remove the DODGY
bit after recomputing gso_segs.If we try to fix two issues, we'd better use separate patches.
quoted hunk ↗ jump to hunk
This change fixes the GSO_UDP_L4 handling case, and remove the DODGY bit at other places. Fixes: 90017accff61 ("sctp: Add GSO support") Fixes: 3820c3f3e417 ("[TCP]: Reset gso_segs if packet is dodgy") Fixes: 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4 packets.") Signed-off-by: Yan Zhai <redacted> --- [1]: https://lore.kernel.org/all/CAJPywTKDdjtwkLVUW6LRA2FU912qcDmQOQGt2WaDo28KzYDg+A@mail.gmail.com/ (local) --- net/ipv4/tcp_offload.c | 1 + net/ipv4/udp_offload.c | 19 +++++++++++++++---- net/ipv6/udp_offload.c | 19 +++++++++++++++---- net/sctp/offload.c | 2 ++ 4 files changed, 33 insertions(+), 8 deletions(-)diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c index 8311c38267b5..f9b93708c22e 100644 --- a/net/ipv4/tcp_offload.c +++ b/net/ipv4/tcp_offload.c@@ -87,6 +87,7 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb, /* Packet is from an untrusted source, reset gso_segs. */ skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss); + skb_shinfo(skb)->gso_type &= ~SKB_GSO_DODGY; segs = NULL; goto out;diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c index 75aa4de5b731..bd29cf19bb6b 100644 --- a/net/ipv4/udp_offload.c +++ b/net/ipv4/udp_offload.c@@ -388,11 +388,22 @@ 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)) - return __udp_gso_segment(skb, features, false); - mss = skb_shinfo(skb)->gso_size; + + if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) { + if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST)) { + /* Packet is from an untrusted source, reset actual gso_segs */ + skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len - sizeof(*uh), + mss); + skb_shinfo(skb)->gso_type &= ~SKB_GSO_DODGY; + + segs = NULL; + goto out; + } else { + return __udp_gso_segment(skb, features, false);
I think it's better and cleaner to move those changes in __udp_gso_segment() as Willem suggests.
quoted hunk ↗ jump to hunk
+ } + } + if (unlikely(skb->len <= mss)) goto out;diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c index ad3b8726873e..6857d9f7bd06 100644 --- a/net/ipv6/udp_offload.c +++ b/net/ipv6/udp_offload.c@@ -43,11 +43,22 @@ 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)) - return __udp_gso_segment(skb, features, true); - mss = skb_shinfo(skb)->gso_size; + + if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) { + if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST)) { + /* Packet is from an untrusted source, reset actual gso_segs */ + skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len - sizeof(*uh), + mss); + skb_shinfo(skb)->gso_type &= ~SKB_GSO_DODGY;
Any reason you want to remove the DODGY here? Is this an optimization? We will lose the chance to recognize/validate it elsewhere. Thanks
quoted hunk ↗ jump to hunk
+ + segs = NULL; + goto out; + } else { + return __udp_gso_segment(skb, features, true); + } + } + if (unlikely(skb->len <= mss)) goto out;diff --git a/net/sctp/offload.c b/net/sctp/offload.c index 502095173d88..3d2b44db0d42 100644 --- a/net/sctp/offload.c +++ b/net/sctp/offload.c@@ -65,6 +65,8 @@ static struct sk_buff *sctp_gso_segment(struct sk_buff *skb, skb_walk_frags(skb, frag_iter) pinfo->gso_segs++; + pinfo->gso_type &= ~SKB_GSO_DODGY; + segs = NULL; goto out; } --2.30.2