[v3,net-next,0/3] ipv6: avoid atomic fragment on GSO output

Message

Yan Zhai Oct. 20, 2023, 5:32 a.m. UTC

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].

The series contains following changes on IPv6 output:
* drop dst_allfrag check, which is always false now
* refactor __ip6_finish_output code to separate GSO and non-GSO packet processing,
  mirroring IPv4 side logic
* avoid generating atomic fragment on GSO packets

Link: https://www.potaroo.net/presentations/2022-03-01-ipv6-frag.pdf [1]

change log:
V2 -> V3: split the changes to separate commits as Willem de Bruijn suggested
V1 is incorrect and omitted

V2: https://lore.kernel.org/netdev/[e-mail]/

Yan Zhai (3):
  ipv6: remove dst_allfrag test on ipv6 output
  ipv6: refactor ip6_finish_output for GSO handling
  ipv6: avoid atomic fragment on GSO packets

 net/ipv6/ip6_output.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)