Re: [PATCH] ipv6: Properly check reference count flag before taking reference

[Petr Vorel]

Hi,

> People are reporting that WireGuard experiences erratic crashes on 5.3,
> and bisected it down to 7d30a7f6424e. Casually flipping through that
> commit I noticed that a flag is checked using `|` instead of `&`, which in
> this current case, means that a reference is never incremented, which
> would result in the use-after-free users are seeing. This commit changes
> the `|` to the proper `&` test.

> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 7d30a7f6424e ("Merge branch 'ipv6-avoid-taking-refcnt-on-dst-during-route-lookup'")
> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>

Reviewed-by: Petr Vorel <pvorel@xxxxxxx>

NOTE: this change was added in d64a1f574a29 ("ipv6: honor RT6_LOOKUP_F_DST_NOREF in rule lookup logic")

Kind regards,
Petr

> ---
>  net/ipv6/ip6_fib.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> index 87f47bc55c5e..6e2af411cd9c 100644
> --- a/net/ipv6/ip6_fib.c
> +++ b/net/ipv6/ip6_fib.c
> @@ -318,7 +318,7 @@ struct dst_entry *fib6_rule_lookup(struct net *net, struct flowi6 *fl6,
>  	if (rt->dst.error == -EAGAIN) {
>  		ip6_rt_put_flags(rt, flags);
>  		rt = net->ipv6.ip6_null_entry;
> -		if (!(flags | RT6_LOOKUP_F_DST_NOREF))
> +		if (!(flags & RT6_LOOKUP_F_DST_NOREF))
>  			dst_hold(&rt->dst);
>  	}