ipv4: Convert ip_route_input() to dscp_t.

Pass a dscp_t variable to ip_route_input(), instead of a plain u8, to
prevent accidental setting of ECN bits in ->flowi4_tos.

Callers of ip_route_input() to consider are:

  * input_action_end_dx4_finish() and input_action_end_dt4() in
    net/ipv6/seg6_local.c. These functions set the tos parameter to 0,
    which is already a valid dscp_t value, so they don't need to be
    adjusted for the new prototype.

  * icmp_route_lookup(), which already has a dscp_t variable to pass as
    parameter. We just need to remove the inet_dscp_to_dsfield()
    conversion.

  * br_nf_pre_routing_finish(), ip_options_rcv_srr() and ip4ip6_err(),
    which get the DSCP directly from IPv4 headers. Define a helper to
    read the .tos field of struct iphdr as dscp_t, so that these
    function don't have to do the conversion manually.

While there, declare *iph as const in br_nf_pre_routing_finish(),
declare its local variables in reverse-christmas-tree order and move
the "err = ip_route_input()" assignment out of the conditional to avoid
checkpatch warning.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/e9d40781d64d3d69f4c79ac8a008b8d67a033e8d.1727807926.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/net/ip.h b/include/net/ip.h
index d92d3bc3ec0e..bab084df1567 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -424,6 +424,11 @@ int ip_decrease_ttl(struct iphdr *iph)
 	return --iph->ttl;
 }
 
+static inline dscp_t ip4h_dscp(const struct iphdr *ip4h)
+{
+	return inet_dsfield_to_dscp(ip4h->tos);
+}
+
 static inline int ip_mtu_locked(const struct dst_entry *dst)
 {
 	const struct rtable *rt = dst_rtable(dst);