Re: kern/60491: arp creates state for invalid messages

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sun, Oct 18, 2026 at 12:27:57PM +0200, Manuel Bouyer wrote:
> On Fri, Oct 16, 2026 at 04:20:02PM +0000, Manuel Bouyer via gnats wrote:
> >  I built a kernel with this patch and rebooted. Let see if we get a
> >  panic ...
> 
> We got a panic:
> login: [ 120230.6352646] panic: kernel diagnostic assertion "op == ARPOP_REPLY || op == ARPOP_REQUEST" failed: file "/dsk/l1/misc/bouyer/HEAD/clean/src/sys/netinet/if_arp.c", line 805 
> [ 120230.6878828] cpu0: Begin traceback...
> [ 120230.6995794] vpanic() at netbsd:vpanic+0x18d
> [ 120230.7062625] kern_assert() at netbsd:kern_assert+0x61
> [ 120230.7278936] in_arpinput() at netbsd:in_arpinput+0x516
> [ 120230.7459382] arpintr() at netbsd:arpintr+0x11c
> [ 120230.7552529] softint_dispatch() at netbsd:softint_dispatch+0x124
> [ 120230.7779701] DDB lost frame for netbsd:Xsoftintr+0x4c, trying 0xffffa380695cd0f0
> [ 120230.7953966] Xsoftintr() at netbsd:Xsoftintr+0x4c
> [ 120230.8159324] --- interrupt ---
> [ 120230.8278898] 0:
> [ 120230.8278898] cpu0: End traceback...

I changed the KASSERT to KASSERTMSG to print op, and got:
login: [ 19315.2724722] panic: kernel diagnostic assertion "op == ARPOP_REPLY || op == ARPOP_REQUEST" failed: file "/dsk/l1/misc/bouyer/HEAD/clean/src/sys/netinet/if_arp.c", line 805 op not REQUEST or REPLY: 65535
[ 19315.3281494] cpu0: Begin traceback...
[ 19315.3400271] vpanic() at netbsd:vpanic+0x18d
[ 19315.3529519] kern_assert() at netbsd:kern_assert+0x61
[ 19315.3624476] in_arpinput() at netbsd:in_arpinput+0x51d
[ 19315.3855787] arpintr() at netbsd:arpintr+0x11c
[ 19315.4025654] softint_dispatch() at netbsd:softint_dispatch+0x124
[ 19315.4134757] DDB lost frame for netbsd:Xsoftintr+0x4c, trying 0xffff8c80695cd0f0
[ 19315.4457469] Xsoftintr() at netbsd:Xsoftintr+0x4c
[ 19315.4531276] --- interrupt ---

The change is:
-       KASSERT(op == ARPOP_REPLY || op == ARPOP_REQUEST);
+       KASSERTMSG(op == ARPOP_REPLY || op == ARPOP_REQUEST,
+           "op not REQUEST or REPLY: %d", op);

Looks like m_makewritable() may be at fault here.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--