ipv4: ip_gre: Fix set but not used warning in ipgre_err() if IPv4-only

if CONFIG_NET_IPGRE is enabled, but CONFIG_IPV6 is disabled:

    net/ipv4/ip_gre.c: In function ‘ipgre_err’:
    net/ipv4/ip_gre.c:144:22: error: variable ‘data_len’ set but not used [-Werror=unused-but-set-variable]
      144 |         unsigned int data_len = 0;
	  |                      ^~~~~~~~

Fix this by moving all data_len processing inside the IPV6-only section
that uses its result.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501121007.2GofXmh5-lkp@intel.com/
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/d09113cfe2bfaca02f3dddf832fb5f48dd20958b.1738704881.git.geert@linux-m68k.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index ed1b6b44faf8049e3f1777c1a32b22b5ed84e4df..c9f11a046c263005dadad9276e2f1abe82fa23cc 100644 (file)
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -141,7 +141,6 @@ static int ipgre_err(struct sk_buff *skb, u32 info,
        const struct iphdr *iph;
        const int type = icmp_hdr(skb)->type;
        const int code = icmp_hdr(skb)->code;
-       unsigned int data_len = 0;
        struct ip_tunnel *t;
 
        if (tpi->proto == htons(ETH_P_TEB))
@@ -182,7 +181,6 @@ static int ipgre_err(struct sk_buff *skb, u32 info,
        case ICMP_TIME_EXCEEDED:
                if (code != ICMP_EXC_TTL)
                        return 0;
-               data_len = icmp_hdr(skb)->un.reserved[1] * 4; /* RFC 4884 4.1 */
                break;
 
        case ICMP_REDIRECT:
@@ -190,10 +188,16 @@ static int ipgre_err(struct sk_buff *skb, u32 info,
        }
 
 #if IS_ENABLED(CONFIG_IPV6)
-       if (tpi->proto == htons(ETH_P_IPV6) &&
-           !ip6_err_gen_icmpv6_unreach(skb, iph->ihl * 4 + tpi->hdr_len,
-                                       type, data_len))
-               return 0;
+       if (tpi->proto == htons(ETH_P_IPV6)) {
+               unsigned int data_len = 0;
+
+               if (type == ICMP_TIME_EXCEEDED)
+                       data_len = icmp_hdr(skb)->un.reserved[1] * 4; /* RFC 4884 4.1 */
+
+               if (!ip6_err_gen_icmpv6_unreach(skb, iph->ihl * 4 + tpi->hdr_len,
+                                               type, data_len))
+                       return 0;
+       }
 #endif
 
        if (t->parms.iph.daddr == 0 ||