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 ---
Thanks to Brett Sheffield for finding the regression and writing the initial fix! --- 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 1f212b2ce4c6..24c898b7654f 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -2575,12 +2575,16 @@ 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;