In the case of TPROXY, bind_conflict optimizations for SO_REUSEADDR or SO_REUSEPORT are broken, possibly resulting in O(n) instead of O(1) bind behaviour or in the incorrect reuse of a bind.
the kernel keeps track for each bind_bucket if all sockets in the bind_bucket support SO_REUSEADDR or SO_REUSEPORT in two fastreuse flags. These flags allow skipping the costly bind_conflict check when possible (meaning when all sockets have the proper SO_REUSE option). For every socket added to a bind_bucket, these flags need to be updated. As soon as a socket that does not support reuse is added, the flag is set to false and will never go back to true, unless the bind_bucket is deleted. Note that there is no mechanism to re-evaluate these flags when a socket is removed (this might make sense when removing a socket that would not allow reuse; this leaves room for a future patch). For this optimization to work, it is mandatory that these flags are properly initialized and updated. When a child socket is created from a listen socket in __inet_inherit_port, the TPROXY case could create a new bind bucket without properly initializing these flags, thus preventing the optimization to work. Alternatively, a socket not allowing reuse could be added to an existing bind bucket without updating the flags, causing bind_conflict to never be called as it should. Patch 1/2 refactors the fastreuse update code in inet_csk_get_port into a small helper function, making the actual fix tiny and easier to understand. Patch 2/2 calls this new helper when __inet_inherit_port decides to create a new bind_bucket or use a different bind_bucket than the one of the listen socket. Tim Froidcoeur (2): net: refactor bind_bucket fastreuse into helper net: initialize fastreuse on inet_inherit_port include/net/inet_connection_sock.h | 4 ++ net/ipv4/inet_connection_sock.c | 99 ++++++++++++++++-------------- net/ipv4/inet_hashtables.c | 1 + 3 files changed, 59 insertions(+), 45 deletions(-) -- 2.25.1 -- Disclaimer: https://www.tessares.net/mail-disclaimer/ <https://www.tessares.net/mail-disclaimer/>
