linux-kernel - [PATCH net-next v2 7/8] rtnetlink: do_setlink: Use struct sockaddr

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Message-Id: <20250521204619.2301870-7-kees@kernel.org>
Date: Wed, 21 May 2025 13:46:15 -0700
From: Kees Cook <kees@...nel.org>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: Kees Cook <kees@...nel.org>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Ido Schimmel <idosch@...dia.com>,
	netdev@...r.kernel.org,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>,
	Chaitanya Kulkarni <kch@...dia.com>,
	Mike Christie <michael.christie@...cle.com>,
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	"Dr. David Alan Gilbert" <linux@...blig.org>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Stanislav Fomichev <sdf@...ichev.me>,
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Subject: [PATCH net-next v2 7/8] 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@...nel.org>
Signed-off-by: Kees Cook <kees@...nel.org>
---
Cc: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>
Cc: Ido Schimmel <idosch@...dia.com>
Cc: <netdev@...r.kernel.org>
---
 net/core/rtnetlink.c | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 9743f1c2ae3c..f9a35bdc58ad 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;
-- 
2.34.1