diff options
| author | Yan Zhai <yan@cloudflare.com> | 2023-10-24 07:26:40 -0700 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2023-10-25 18:04:29 -0700 |
| commit | 03d6c848bfb406e9ef6d9846d759e97beaeea113 (patch) | |
| tree | 9283e779aab9e7621bb9ae824dcadb28f699096e /net/ipv6 | |
| parent | 1f7ec1b3721d7f49f13d01e6f5ed5f28a305e3b6 (diff) | |
ipv6: avoid atomic fragment on GSO packets
When the ipv6 stack output a GSO packet, if its gso_size is larger than
dst MTU, then all segments would be fragmented. However, it is possible
for a GSO packet to have a trailing segment with smaller actual size
than both gso_size as well as the MTU, which leads to an "atomic
fragment". Atomic fragments are considered harmful in RFC-8021. An
Existing report from APNIC also shows that atomic fragments are more
likely to be dropped even it is equivalent to a no-op [1].
Add an extra check in the GSO slow output path. For each segment from
the original over-sized packet, if it fits with the path MTU, then avoid
generating an atomic fragment.
Link: https://www.potaroo.net/presentations/2022-03-01-ipv6-frag.pdf [1]
Fixes: b210de4f8c97 ("net: ipv6: Validate GSO SKB before finish IPv6 processing")
Reported-by: David Wragg <dwragg@cloudflare.com>
Signed-off-by: Yan Zhai <yan@cloudflare.com>
Link: https://lore.kernel.org/r/90912e3503a242dca0bc36958b11ed03a2696e5e.1698156966.git.yan@cloudflare.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/ipv6')
| -rw-r--r-- | net/ipv6/ip6_output.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index 4010dd97aaf8..a722a43dd668 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -164,7 +164,13 @@ ip6_finish_output_gso_slowpath_drop(struct net *net, struct sock *sk, int err; skb_mark_not_on_list(segs); - err = ip6_fragment(net, sk, segs, ip6_finish_output2); + /* Last GSO segment can be smaller than gso_size (and MTU). + * Adding a fragment header would produce an "atomic fragment", + * which is considered harmful (RFC-8021). Avoid that. + */ + err = segs->len > mtu ? + ip6_fragment(net, sk, segs, ip6_finish_output2) : + ip6_finish_output2(net, sk, segs); if (err && ret == 0) ret = err; } |