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Message-ID: <04d904dc-b64a-a6b7-9f0e-40c3d9a2e6a3@gmail.com> Date: Wed, 1 May 2019 17:01:05 -0400 From: Eric Dumazet <eric.dumazet@...il.com> To: Martin KaFai Lau <kafai@...com>, netdev@...r.kernel.org Cc: David Ahern <dsahern@...il.com>, David Miller <davem@...emloft.net>, Jonathan Lemon <bsd@...com>, kernel-team@...com, Wei Wang <weiwan@...gle.com> Subject: Re: [PATCH net] ipv6: A few fixes on dereferencing rt->from On 4/30/19 10:45 AM, Martin KaFai Lau wrote: > It is a followup after the fix in > commit 9c69a1320515 ("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: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected") > Signed-off-by: Martin KaFai Lau <kafai@...com> > --- > Reviewed-by: Eric Dumazet <edumazet@...gle.com>
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