[PATCH] netlink: Allow NULL to be passed as addr parameter to nl_addr_get (again)

[PATCH] netlink: Allow NULL to be passed as addr parameter to nl_addr_get (again)

[David Gibson]

A recent fix to nl_addr_get() unfortunately introduced a different problem.
251e676bd0bf removed a test if @addr was non-NULL.  conf_ip6() relied on
being able to pass NULL in order to update the link-local address without
updating the main address (because it was already set by the user).

This means that 'pasta -a 2001:db8::1' will SEGV.  Reverse the incorrect
part of the change to fix this.

Fixes: 251e676bd0bf ("netlink: Return prefix length for IPv6 addresses in nl_addr_get()")
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 netlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/netlink.c b/netlink.c
index ee9a6b16..e07b47f4 100644
--- a/netlink.c
+++ b/netlink.c
@@ -788,7 +788,7 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
 			    (af == AF_INET6 && rta->rta_type != IFA_ADDRESS))
 				continue;
 
-			if (ifa->ifa_prefixlen > prefix_max &&
+			if (ifa->ifa_prefixlen > prefix_max && addr &&
 			    (af == AF_INET || ifa->ifa_scope < RT_SCOPE_LINK)) {
 				memcpy(addr, RTA_DATA(rta), RTA_PAYLOAD(rta));
 
-- 
2.53.0

Re: [PATCH] netlink: Allow NULL to be passed as addr parameter to nl_addr_get (again)

[Stefano Brivio]

On Wed, 11 Mar 2026 15:13:57 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> A recent fix to nl_addr_get() unfortunately introduced a different problem.
> 251e676bd0bf removed a test if @addr was non-NULL.  conf_ip6() relied on
> being able to pass NULL in order to update the link-local address without
> updating the main address (because it was already set by the user).
> 
> This means that 'pasta -a 2001:db8::1' will SEGV.  Reverse the incorrect
> part of the change to fix this.

Ouch, sorry. I totally misinterpreted the check on 'addr' (my own
check, by the way) and suggested to Jon that it could be skipped.

> Fixes: 251e676bd0bf ("netlink: Return prefix length for IPv6 addresses in nl_addr_get()")
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Applied.

-- 
Stefano