[PATCH] net: ipv4: fix regression in local-broadcast routes

[PATCH] net: ipv4: fix regression in local-broadcast routes

[Chanho Min]

From: Oscar Maes <oscmaes92@gmail.com>

[ Upstream commit 5189446ba995556eaa3755a6e875bc06675b88bd ]

Commit 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
introduced a regression where local-broadcast packets would have their
gateway set in __mkroute_output, which was caused by fi = NULL being
removed.

Fix this by resetting the fib_info for local-broadcast packets. This
preserves the intended changes for directed-broadcast packets.

Cc: stable@vger.kernel.org
Fixes: 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
Reported-by: Brett A C Sheffield <bacs@librecast.net>
Closes: https://lore.kernel.org/regressions/20250822165231.4353-4-bacs@librecast.net
Signed-off-by: Oscar Maes <oscmaes92@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250827062322.4807-1-oscmaes92@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv4/route.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 9a5c9497b393..261ddb6542a4 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2532,12 +2532,16 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
 		    !netif_is_l3_master(dev_out))
 			return ERR_PTR(-EINVAL);
 
-	if (ipv4_is_lbcast(fl4->daddr))
+	if (ipv4_is_lbcast(fl4->daddr)) {
 		type = RTN_BROADCAST;
-	else if (ipv4_is_multicast(fl4->daddr))
+
+		/* reset fi to prevent gateway resolution */
+		fi = NULL;
+	} else if (ipv4_is_multicast(fl4->daddr)) {
 		type = RTN_MULTICAST;
-	else if (ipv4_is_zeronet(fl4->daddr))
+	} else if (ipv4_is_zeronet(fl4->daddr)) {
 		return ERR_PTR(-EINVAL);
+	}
 
 	if (dev_out->flags & IFF_LOOPBACK)
 		flags |= RTCF_LOCAL;

Re: [PATCH] net: ipv4: fix regression in local-broadcast routes

[민찬호/책임연구원/SW Platform(연)Advanced OS TP]

Hi all,

Please ignore my previous email. It was sent to the list by mistake.

Sorry for the noise.

Thanks,
Chanho Min

________________________________________
보낸 사람: Chanho Min <chanho.min@lge.com>
보낸 날짜: 2025년 12월 23일 화요일 15:59
받는 사람: 민찬호/책임연구원/SW Platform(연)Advanced OS TP
참조: Oscar Maes; stable@vger.kernel.org; Paolo Abeni; Sasha Levin
제목: [PATCH] net: ipv4: fix regression in local-broadcast routes

From: Oscar Maes <oscmaes92@gmail.com>

[ Upstream commit 5189446ba995556eaa3755a6e875bc06675b88bd ]

Commit 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
introduced a regression where local-broadcast packets would have their
gateway set in __mkroute_output, which was caused by fi = NULL being
removed.

Fix this by resetting the fib_info for local-broadcast packets. This
preserves the intended changes for directed-broadcast packets.

Cc: stable@vger.kernel.org
Fixes: 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
Reported-by: Brett A C Sheffield <bacs@librecast.net>
Closes: https://lore.kernel.org/regressions/20250822165231.4353-4-bacs@librecast.net
Signed-off-by: Oscar Maes <oscmaes92@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250827062322.4807-1-oscmaes92@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv4/route.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 9a5c9497b393..261ddb6542a4 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2532,12 +2532,16 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
                    !netif_is_l3_master(dev_out))
                        return ERR_PTR(-EINVAL);

-       if (ipv4_is_lbcast(fl4->daddr))
+       if (ipv4_is_lbcast(fl4->daddr)) {
                type = RTN_BROADCAST;
-       else if (ipv4_is_multicast(fl4->daddr))
+
+               /* reset fi to prevent gateway resolution */
+               fi = NULL;
+       } else if (ipv4_is_multicast(fl4->daddr)) {
                type = RTN_MULTICAST;
-       else if (ipv4_is_zeronet(fl4->daddr))
+       } else if (ipv4_is_zeronet(fl4->daddr)) {
                return ERR_PTR(-EINVAL);
+       }

        if (dev_out->flags & IFF_LOOPBACK)
                flags |= RTCF_LOCAL;

Re: [PATCH] net: ipv4: fix regression in local-broadcast routes

[Greg KH]

On Tue, Dec 23, 2025 at 03:59:11PM +0900, Chanho Min wrote:
> From: Oscar Maes <oscmaes92@gmail.com>
> 
> [ Upstream commit 5189446ba995556eaa3755a6e875bc06675b88bd ]
> 
> Commit 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
> introduced a regression where local-broadcast packets would have their
> gateway set in __mkroute_output, which was caused by fi = NULL being
> removed.
> 
> Fix this by resetting the fib_info for local-broadcast packets. This
> preserves the intended changes for directed-broadcast packets.
> 
> Cc: stable@vger.kernel.org
> Fixes: 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
> Reported-by: Brett A C Sheffield <bacs@librecast.net>
> Closes: https://lore.kernel.org/regressions/20250822165231.4353-4-bacs@librecast.net
> Signed-off-by: Oscar Maes <oscmaes92@gmail.com>
> Reviewed-by: David Ahern <dsahern@kernel.org>
> Link: https://patch.msgid.link/20250827062322.4807-1-oscmaes92@gmail.com
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  net/ipv4/route.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)

You forgot to sign off on this :(

Also, what tree do you want this backported to?

thanks,

greg k-h

Re: [PATCH] net: ipv4: fix regression in local-broadcast routes

[Chanho Min]

On Tue, Dec 23, 2025 at 08:44:32AM +0100, Greg KH wrote:
> On Tue, Dec 23, 2025 at 03:59:11PM +0900, Chanho Min wrote:
> > From: Oscar Maes <oscmaes92@gmail.com>
> > 
> > [ Upstream commit 5189446ba995556eaa3755a6e875bc06675b88bd ]
> > 
> > Commit 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
> > introduced a regression where local-broadcast packets would have their
> > gateway set in __mkroute_output, which was caused by fi = NULL being
> > removed.
> > 
> > Fix this by resetting the fib_info for local-broadcast packets. This
> > preserves the intended changes for directed-broadcast packets.
> > 
> > Cc: stable@vger.kernel.org
> > Fixes: 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
> > Reported-by: Brett A C Sheffield <bacs@librecast.net>
> > Closes: https://lore.kernel.org/regressions/20250822165231.4353-4-bacs@librecast.net
> > Signed-off-by: Oscar Maes <oscmaes92@gmail.com>
> > Reviewed-by: David Ahern <dsahern@kernel.org>
> > Link: https://patch.msgid.link/20250827062322.4807-1-oscmaes92@gmail.com
> > Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > ---
> >  net/ipv4/route.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> You forgot to sign off on this :(
> 
> Also, what tree do you want this backported to?
> 
> thanks,
> 
> greg k-h


Please ignore this patch. It was sent to the list by mistake.

Sorry for the noise.

Thanks,
Chanho Min