Check if fib6_nh is non-NULL before accessing fib6_nh->fib_nh_gw_family
in ipv6_route_native_seq_show() to prevent a null-pointer dereference.
Assign dev as dev = fib6_nh ? fib6_nh->fib_nh_dev : NULL to ensure safe
handling when nexthop_fib6_nh(rt->nh) returns NULL.

Fixes: 0379e8e6a9ef ("ipv6: ip6_fib: avoid NPD in ipv6_route_native_seq_show()")

Signed-off-by: Yi Zou <03zouyi09.25@gmail.com>
---
 net/ipv6/ip6_fib.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index eb111d20615c..6632ab65d206 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -2555,14 +2555,14 @@ static int ipv6_route_native_seq_show(struct seq_file *seq, void *v)
 #else
 	seq_puts(seq, "00000000000000000000000000000000 00 ");
 #endif
-	if (fib6_nh->fib_nh_gw_family) {
+	if (fib6_nh && fib6_nh->fib_nh_gw_family) {
 		flags |= RTF_GATEWAY;
 		seq_printf(seq, "%pi6", &fib6_nh->fib_nh_gw6);
 	} else {
 		seq_puts(seq, "00000000000000000000000000000000");
 	}
 
-	dev = fib6_nh->fib_nh_dev;
+	dev = fib6_nh ? fib6_nh->fib_nh_dev : NULL;
 	seq_printf(seq, " %08x %08x %08x %08x %8s\n",
 		   rt->fib6_metric, refcount_read(&rt->fib6_ref), 0,
 		   flags, dev ? dev->name : "");
-- 
2.44.0

On Sat, Nov 2, 2024 at 9:08 PM Yi Zou <03zouyi09.25@gmail.com> wrote:
>
> Check if fib6_nh is non-NULL before accessing fib6_nh->fib_nh_gw_family
> in ipv6_route_native_seq_show() to prevent a null-pointer dereference.
> Assign dev as dev = fib6_nh ? fib6_nh->fib_nh_dev : NULL to ensure safe
> handling when nexthop_fib6_nh(rt->nh) returns NULL.
>
> Fixes: 0379e8e6a9ef ("ipv6: ip6_fib: avoid NPD in ipv6_route_native_seq_show()")

I could not find this commit in upstream trees.

Please make sure to sort out the details before sending a patch.

On Sun,  3 Nov 2024 04:08:20 +0800 Yi Zou wrote:
> Check if fib6_nh is non-NULL before accessing fib6_nh->fib_nh_gw_family
> in ipv6_route_native_seq_show() to prevent a null-pointer dereference.
> Assign dev as dev = fib6_nh ? fib6_nh->fib_nh_dev : NULL to ensure safe
> handling when nexthop_fib6_nh(rt->nh) returns NULL.

Are you just sending this patch because nexthop_fib6_nh() may return
NULL? Not sure it can happen since we know we're walking a v6-only
table here.

Please try to crash it and add a stack trace to the commit message. 

BTW your last posting was white space damaged. Stick to git send-email