On Fri, Sep 06, 2024 at 05:55:13PM +0300, Andy Shevchenko wrote:
> In some cases (CONFIG_BRIDGE_NETFILTER=n) the pointer to IP header
> is set but not used, it prevents kernel builds with clang, `make W=1`
> and CONFIG_WERROR=y:
>
> ipv6: split nf_send_reset6() in smaller functions
> netfilter: nf_reject_ipv4: split nf_send_reset() in smaller functions
>
> net/ipv4/netfilter/nf_reject_ipv4.c:243:16: error: variable 'niph' set but not used [-Werror,-Wunused-but-set-variable]
> 243 | struct iphdr *niph;
> | ^
> net/ipv6/netfilter/nf_reject_ipv6.c:286:18: error: variable 'ip6h' set but not used [-Werror,-Wunused-but-set-variable]
> 286 | struct ipv6hdr *ip6h;
> | ^
>
> Fix these by marking respective variables with __maybe_unused as it
> seems more complicated to address that in a better way due to ifdeffery.
>
> Fixes: 8bfcdf6671b1 ("netfilter: nf_reject_ipv6: split nf_send_reset6() in smaller functions")
> Fixes: 052b9498eea5 ("netfilter: nf_reject_ipv4: split nf_send_reset() in smaller functions")
Hi Andy,
As mentioned in relation to another similar patch,
I'm not sure that resolution of W=1 warnings are fixes.
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> ---
> net/ipv4/netfilter/nf_reject_ipv4.c | 2 +-
> net/ipv6/netfilter/nf_reject_ipv6.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
> index 04504b2b51df..0af42494ac66 100644
> --- a/net/ipv4/netfilter/nf_reject_ipv4.c
> +++ b/net/ipv4/netfilter/nf_reject_ipv4.c
> @@ -240,7 +240,7 @@ void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
> int hook)
> {
> struct sk_buff *nskb;
> - struct iphdr *niph;
> + struct iphdr *niph __maybe_unused;
> const struct tcphdr *oth;
> struct tcphdr _oth;
>
Possibly it is broken for some reason - like reading nskb too late -
but I wonder if rather than annotating niph it's scope can be reduced
to the code that is only compiled if CONFIG_BRIDGE_NETFILTER is enabled.
This also addreses what appears to be an assingment of niph without
the value being used - the first assingment.
E.g., for the ipv4 case (compile tested only!):
diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index 04504b2b51df..87fd945a0d27 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -239,9 +239,8 @@ static int nf_reject_fill_skb_dst(struct sk_buff *skb_in)
void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
int hook)
{
- struct sk_buff *nskb;
- struct iphdr *niph;
const struct tcphdr *oth;
+ struct sk_buff *nskb;
struct tcphdr _oth;
oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
@@ -266,14 +265,12 @@ void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
nskb->mark = IP4_REPLY_MARK(net, oldskb->mark);
skb_reserve(nskb, LL_MAX_HEADER);
- niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
- ip4_dst_hoplimit(skb_dst(nskb)));
+ nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
+ ip4_dst_hoplimit(skb_dst(nskb)));
nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
if (ip_route_me_harder(net, sk, nskb, RTN_UNSPEC))
goto free_nskb;
- niph = ip_hdr(nskb);
-
/* "Never happens" */
if (nskb->len > dst_mtu(skb_dst(nskb)))
goto free_nskb;
@@ -290,6 +287,7 @@ void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
*/
if (nf_bridge_info_exists(oldskb)) {
struct ethhdr *oeth = eth_hdr(oldskb);
+ struct iphdr *niph = ip_hdr(nskb);
struct net_device *br_indev;
br_indev = nf_bridge_get_physindev(oldskb, net);
