[PATCH] rtnetlink: do_setlink: Use true struct sockaddr

From: Kees Cook
Date: Mon Dec 16 2024 - 21:05:03 EST


Instead of a heap allocation use a stack allocated struct sockaddr, as
dev_set_mac_address_user() is the consumer (which uses a classic
struct sockaddr). Cap the copy to the minimum address size between
the incoming address and the traditional sa_data field itself.

Putting "sa" on the stack means it will get a reused stack slot since
it is smaller than other existing single-scope stack variables (like
the vfinfo array).

Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
---
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: Ido Schimmel <idosch@xxxxxxxxxx>
Cc: Petr Machata <petrm@xxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
---
net/core/rtnetlink.c | 22 +++++++---------------
1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index ab5f201bf0ab..6da0edc0870d 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -3048,21 +3048,13 @@ 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;
- memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
- dev->addr_len);
- err = dev_set_mac_address_user(dev, sa, extack);
- kfree(sa);
+ struct sockaddr sa = { };
+
+ /* dev_set_mac_address_user() uses a true struct sockaddr. */
+ sa.sa_family = dev->type;
+ memcpy(sa.sa_data, nla_data(tb[IFLA_ADDRESS]),
+ min(dev->addr_len, sizeof(sa.sa_data_min)));
+ err = dev_set_mac_address_user(dev, &sa, extack);
if (err)
goto errout;
status |= DO_SETLINK_MODIFIED;
--
2.34.1