[PATCH 7/7] rtnetlink: do_setlink: Use struct sockaddr_storage

Kees Cook
2025-05-20T22:31:15Z

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.

Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Ido Schimmel <idosch@nvidia.com>
Cc: <netdev@vger.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