It is a followup after the fix in
commit 9c69a13205 ("route: Avoid crash from dereferencing NULL rt->from")
rt6_do_redirect():
1. NULL checking is needed on rt->from because a parallel
fib6_info delete could happen that sets rt->from to NULL.
(e.g. rt6_remove_exception() and fib6_drop_pcpu_from()).
2. fib6_info_hold() is not enough. Same reason as (1).
Meaning, holding dst->__refcnt cannot ensure
rt->from is not NULL or rt->from->fib6_ref is not 0.
Instead of using fib6_info_hold_safe() which ip6_rt_cache_alloc()
is already doing, this patch chooses to extend the rcu section
to keep "from" dereference-able after checking for NULL.
inet6_rtm_getroute():
1. NULL checking is also needed on rt->from for a similar reason.
Note that inet6_rtm_getroute() is using RTNL_FLAG_DOIT_UNLOCKED.
Fixes: a68886a691 ("net/ipv6: Make from in rt6_info rcu protected")
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Wei Wang <weiwan@google.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
886b7a5010