From: Wei Wang weiwan@google.com
[ Upstream commit 5018c59607a511cdee743b629c76206d9c9e6d7b ]
Jesse and Ido reported the following race condition: <CPU A, t0> - Received packet A is forwarded and cached dst entry is taken from the nexthop ('nhc->nhc_rth_input'). Calls skb_dst_set()
<t1> - Given Jesse has busy routers ("ingesting full BGP routing tables from multiple ISPs"), route is added / deleted and rt_cache_flush() is called
<CPU B, t2> - Received packet B tries to use the same cached dst entry from t0, but rt_cache_valid() is no longer true and it is replaced in rt_cache_route() by the newer one. This calls dst_dev_put() on the original dst entry which assigns the blackhole netdev to 'dst->dev'
<CPU A, t3> - dst_input(skb) is called on packet A and it is dropped due to 'dst->dev' being the blackhole netdev
There are 2 issues in the v4 routing code: 1. A per-netns counter is used to do the validation of the route. That means whenever a route is changed in the netns, users of all routes in the netns needs to redo lookup. v6 has an implementation of only updating fn_sernum for routes that are affected. 2. When rt_cache_valid() returns false, rt_cache_route() is called to throw away the current cache, and create a new one. This seems unnecessary because as long as this route does not change, the route cache does not need to be recreated.
To fully solve the above 2 issues, it probably needs quite some code changes and requires careful testing, and does not suite for net branch.
So this patch only tries to add the deleted cached rt into the uncached list, so user could still be able to use it to receive packets until it's done.
Fixes: 95c47f9cf5e0 ("ipv4: call dst_dev_put() properly") Signed-off-by: Wei Wang weiwan@google.com Reported-by: Ido Schimmel idosch@idosch.org Reported-by: Jesse Hathaway jesse@mbuki-mvuki.org Tested-by: Jesse Hathaway jesse@mbuki-mvuki.org Acked-by: Martin KaFai Lau kafai@fb.com Cc: David Ahern dsahern@gmail.com Reviewed-by: Ido Schimmel idosch@mellanox.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/route.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1476,7 +1476,7 @@ static bool rt_cache_route(struct fib_nh prev = cmpxchg(p, orig, rt); if (prev == orig) { if (orig) { - dst_dev_put(&orig->dst); + rt_add_uncached_list(orig); dst_release(&orig->dst); } } else {