[PATCH net-next] ipv4: Prepare inet_rtm_getroute() to .flowi4_tos conversion.

[PATCH net-next] ipv4: Prepare inet_rtm_getroute() to .flowi4_tos conversion.

[Guillaume Nault]

Store rtm->rtm_tos in a dscp_t variable, which can then be used for
setting fl4.flowi4_tos and also be passed as parameter of
ip_route_input_rcu().

The .flowi4_tos field is going to be converted to dscp_t to ensure ECN
bits aren't erroneously taken into account during route lookups. Having
a dscp_t variable available will simplify that conversion, as we'll
just have to drop the inet_dscp_to_dsfield() call.

Note that we can't just convert rtm->rtm_tos to dscp_t because this
structure is exported to user space.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
---
 net/ipv4/route.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 9f9d4e6ea1b9..1f7e2a02dd25 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -3269,6 +3269,7 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 	struct flowi4 fl4 = {};
 	__be32 dst = 0;
 	__be32 src = 0;
+	dscp_t dscp;
 	kuid_t uid;
 	u32 iif;
 	int err;
@@ -3283,6 +3284,7 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 	dst = nla_get_in_addr_default(tb[RTA_DST], 0);
 	iif = nla_get_u32_default(tb[RTA_IIF], 0);
 	mark = nla_get_u32_default(tb[RTA_MARK], 0);
+	dscp = inet_dsfield_to_dscp(rtm->rtm_tos);
 	if (tb[RTA_UID])
 		uid = make_kuid(current_user_ns(), nla_get_u32(tb[RTA_UID]));
 	else
@@ -3307,7 +3309,7 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 
 	fl4.daddr = dst;
 	fl4.saddr = src;
-	fl4.flowi4_tos = rtm->rtm_tos & INET_DSCP_MASK;
+	fl4.flowi4_tos = inet_dscp_to_dsfield(dscp);
 	fl4.flowi4_oif = nla_get_u32_default(tb[RTA_OIF], 0);
 	fl4.flowi4_mark = mark;
 	fl4.flowi4_uid = uid;
@@ -3331,9 +3333,8 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 		fl4.flowi4_iif = iif; /* for rt_fill_info */
 		skb->dev	= dev;
 		skb->mark	= mark;
-		err = ip_route_input_rcu(skb, dst, src,
-					 inet_dsfield_to_dscp(rtm->rtm_tos),
-					 dev, &res) ? -EINVAL : 0;
+		err = ip_route_input_rcu(skb, dst, src, dscp, dev,
+					 &res) ? -EINVAL : 0;
 
 		rt = skb_rtable(skb);
 		if (err == 0 && rt->dst.error)
-- 
2.39.2

Re: [PATCH net-next] ipv4: Prepare inet_rtm_getroute() to .flowi4_tos conversion.

[Ido Schimmel]

On Wed, Jan 15, 2025 at 01:44:52PM +0100, Guillaume Nault wrote:
> Store rtm->rtm_tos in a dscp_t variable, which can then be used for
> setting fl4.flowi4_tos and also be passed as parameter of
> ip_route_input_rcu().
> 
> The .flowi4_tos field is going to be converted to dscp_t to ensure ECN
> bits aren't erroneously taken into account during route lookups. Having
> a dscp_t variable available will simplify that conversion, as we'll
> just have to drop the inet_dscp_to_dsfield() call.
> 
> Note that we can't just convert rtm->rtm_tos to dscp_t because this
> structure is exported to user space.
> 
> Signed-off-by: Guillaume Nault <gnault@redhat.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

Re: [PATCH net-next] ipv4: Prepare inet_rtm_getroute() to .flowi4_tos conversion.

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 15 Jan 2025 13:44:52 +0100 you wrote:
> Store rtm->rtm_tos in a dscp_t variable, which can then be used for
> setting fl4.flowi4_tos and also be passed as parameter of
> ip_route_input_rcu().
> 
> The .flowi4_tos field is going to be converted to dscp_t to ensure ECN
> bits aren't erroneously taken into account during route lookups. Having
> a dscp_t variable available will simplify that conversion, as we'll
> just have to drop the inet_dscp_to_dsfield() call.
> 
> [...]

Here is the summary with links:
  - [net-next] ipv4: Prepare inet_rtm_getroute() to .flowi4_tos conversion.
    https://git.kernel.org/netdev/net-next/c/65a55aa7e64e

You are awesome, thank you!
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