From: Kees Cook <kees@kernel.org>
Date: Wed, 21 May 2025 20:46:15 +0000 (-0700)
Subject: rtnetlink: do_setlink: Use struct sockaddr_storage
X-Git-Tag: v6.16-rc1~132^2~28^2~1
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6b12e0a3c3c9565c7dc106e2a8b1d433b1aa8eb6;p=thirdparty%2Fkernel%2Flinux.git

rtnetlink: do_setlink: Use struct sockaddr_storage

Instead of a heap allocating a variably sized struct sockaddr and lying
about the type in the call to netif_set_mac_address(), use a stack
allocated struct sockaddr_storage. This lets us drop the cast and avoid
the allocation.

Putting "ss" on the stack means it will get a reused stack slot since
it is the same size (128B) as other existing single-scope stack variables,
like the vfinfo array (128B), so no additional stack space is used by
this function.

Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Kees Cook <kees@kernel.org>
Link: https://patch.msgid.link/20250521204619.2301870-7-kees@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 9743f1c2ae3c3..f9a35bdc58ad2 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -3080,17 +3080,7 @@ static int do_setlink(const struct sk_buff *skb, struct net_device *dev,
 	}
 
 	if (tb[IFLA_ADDRESS]) {
-		struct sockaddr *sa;
-		int len;
-
-		len = sizeof(sa_family_t) + max_t(size_t, dev->addr_len,
-						  sizeof(*sa));
-		sa = kmalloc(len, GFP_KERNEL);
-		if (!sa) {
-			err = -ENOMEM;
-			goto errout;
-		}
-		sa->sa_family = dev->type;
+		struct sockaddr_storage ss = { };
 
 		netdev_unlock_ops(dev);
 
@@ -3098,10 +3088,9 @@ static int do_setlink(const struct sk_buff *skb, struct net_device *dev,
 		down_write(&dev_addr_sem);
 		netdev_lock_ops(dev);
 
-		memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
-		       dev->addr_len);
-		err = netif_set_mac_address(dev, (struct sockaddr_storage *)sa, extack);
-		kfree(sa);
+		ss.ss_family = dev->type;
+		memcpy(ss.__data, nla_data(tb[IFLA_ADDRESS]), dev->addr_len);
+		err = netif_set_mac_address(dev, &ss, extack);
 		if (err) {
 			up_write(&dev_addr_sem);
 			goto errout;