The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 61fb0d01680771f72cc9d39783fb2c122aaad51e Mon Sep 17 00:00:00 2001

From: Eric Dumazet edumazet@google.com Date: Wed, 15 May 2019 19:39:52 -0700 Subject: [PATCH] ipv6: prevent possible fib6 leaks

At ipv6 route dismantle, fib6_drop_pcpu_from() is responsible for finding all percpu routes and set their ->from pointer to NULL, so that fib6_ref can reach its expected value (1).

The problem right now is that other cpus can still catch the route being deleted, since there is no rcu grace period between the route deletion and call to fib6_drop_pcpu_from()

This can leak the fib6 and associated resources, since no notifier will take care of removing the last reference(s).

I decided to add another boolean (fib6_destroying) instead of reusing/renaming exception_bucket_flushed to ease stable backports, and properly document the memory barriers used to implement this fix.

This patch has been co-developped with Wei Wang.

Fixes: 93531c674315 ("net/ipv6: separate handling of FIB entries from dst based routes") Signed-off-by: Eric Dumazet edumazet@google.com Reported-by: syzbot syzkaller@googlegroups.com Cc: Wei Wang weiwan@google.com Cc: David Ahern dsahern@gmail.com Cc: Martin Lau kafai@fb.com Acked-by: Wei Wang weiwan@google.com Acked-by: Martin KaFai Lau kafai@fb.com Reviewed-by: David Ahern dsahern@gmail.com Signed-off-by: David S. Miller davem@davemloft.net

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h index 40105738e2f6..525f701653ca 100644 --- a/include/net/ip6_fib.h +++ b/include/net/ip6_fib.h @@ -167,7 +167,8 @@ struct fib6_info { dst_nocount:1, dst_nopolicy:1, dst_host:1, - unused:3; + fib6_destroying:1, + unused:2;

struct fib6_nh fib6_nh; struct rcu_head rcu; diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index 08e0390e001c..008421b550c6 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -904,6 +904,12 @@ static void fib6_drop_pcpu_from(struct fib6_info *f6i, { int cpu;

+ /* Make sure rt6_make_pcpu_route() wont add other percpu routes + * while we are cleaning them here. + */ + f6i->fib6_destroying = 1; + mb(); /* paired with the cmpxchg() in rt6_make_pcpu_route() */ + /* release the reference to this fib entry from * all of its cached pcpu routes */ @@ -927,6 +933,9 @@ static void fib6_purge_rt(struct fib6_info *rt, struct fib6_node *fn, { struct fib6_table *table = rt->fib6_table;

+ if (rt->rt6i_pcpu) + fib6_drop_pcpu_from(rt, table); + if (refcount_read(&rt->fib6_ref) != 1) { /* This route is used as dummy address holder in some split * nodes. It is not leaked, but it still holds other resources, @@ -948,9 +957,6 @@ static void fib6_purge_rt(struct fib6_info *rt, struct fib6_node *fn, fn = rcu_dereference_protected(fn->parent, lockdep_is_held(&table->tb6_lock)); } - - if (rt->rt6i_pcpu) - fib6_drop_pcpu_from(rt, table); } }

diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 23a20d62daac..27c0cc5d9d30 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1295,6 +1295,13 @@ static struct rt6_info *rt6_make_pcpu_route(struct net *net, prev = cmpxchg(p, NULL, pcpu_rt); BUG_ON(prev);

+ if (res->f6i->fib6_destroying) { + struct fib6_info *from; + + from = xchg((__force struct fib6_info **)&pcpu_rt->from, NULL); + fib6_info_release(from); + } + return pcpu_rt; }