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

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

[Jason A. Donenfeld]

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@vger.kernel.org
Fixes: 7d30a7f6424e ("Merge branch 'ipv6-avoid-taking-refcnt-on-dst-during-route-lookup'")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 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);
 	}
 
-- 
2.21.0

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@vger.kernel.org
> Fixes: 7d30a7f6424e ("Merge branch 'ipv6-avoid-taking-refcnt-on-dst-during-route-lookup'")
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Reviewed-by: Petr Vorel <pvorel@suse.cz>

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);
>  	}

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

[Jason A. Donenfeld]

Apparently even with this (certainly correct) patch attached, users
are still experiencing problems. Bug hunting continues, and I'll
report back if I figure something out.

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

[Eric Dumazet]

On 9/23/19 8:06 AM, Petr Vorel wrote:
> 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@vger.kernel.org
>> Fixes: 7d30a7f6424e ("Merge branch 'ipv6-avoid-taking-refcnt-on-dst-during-route-lookup'")
>> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> 
> Reviewed-by: Petr Vorel <pvorel@suse.cz>
> 
> NOTE: this change was added in d64a1f574a29 ("ipv6: honor RT6_LOOKUP_F_DST_NOREF in rule lookup logic")
> 
> Kind regards,
> Petr
> 

This was fixed earlier I think

https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/?id=7b09c2d052db4b4ad0b27b97918b46a7746966fa

>> ---
>>  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);
>>  	}