[PATCH net-next] ip: silence udp zerocopy smatch false positive

[PATCH net-next] ip: silence udp zerocopy smatch false positive

[Willem de Bruijn]

From: Willem de Bruijn <willemb@google.com>

extra_uref is used in __ip(6)_append_data only if uarg is set.

Smatch sees that the variable is passed to sock_zerocopy_put_abort.
This function accesses it only when uarg is set, but smatch cannot
infer this.

Make this dependency explicit.

Fixes: 52900d22288e ("udp: elide zerocopy operation in hot path")
Signed-off-by: Willem de Bruijn <willemb@google.com>
---
 net/ipv4/ip_output.c  | 3 ++-
 net/ipv6/ip6_output.c | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 78f028bdad30b..ab6618036afed 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1130,7 +1130,8 @@ static int __ip_append_data(struct sock *sk,
 error_efault:
 	err = -EFAULT;
 error:
-	sock_zerocopy_put_abort(uarg, extra_uref);
+	if (uarg)
+		sock_zerocopy_put_abort(uarg, extra_uref);
 	cork->length -= length;
 	IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTDISCARDS);
 	refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 6592a39e5ec10..be25b34dc5c2f 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1575,7 +1575,8 @@ static int __ip6_append_data(struct sock *sk,
 error_efault:
 	err = -EFAULT;
 error:
-	sock_zerocopy_put_abort(uarg, extra_uref);
+	if (uarg)
+		sock_zerocopy_put_abort(uarg, extra_uref);
 	cork->length -= length;
 	IP6_INC_STATS(sock_net(sk), rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS);
 	refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);
-- 
2.20.0.rc2.403.gdbc3b29805-goog

Re: [PATCH net-next] ip: silence udp zerocopy smatch false positive

[David Miller]

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: Sat,  8 Dec 2018 06:22:46 -0500

> From: Willem de Bruijn <willemb@google.com>
> 
> extra_uref is used in __ip(6)_append_data only if uarg is set.
> 
> Smatch sees that the variable is passed to sock_zerocopy_put_abort.
> This function accesses it only when uarg is set, but smatch cannot
> infer this.
> 
> Make this dependency explicit.
> 
> Fixes: 52900d22288e ("udp: elide zerocopy operation in hot path")
> Signed-off-by: Willem de Bruijn <willemb@google.com>

I looked and can't figure out a better way to fix this :)

Applied, thanks Willem.