Re: [PATCH RFC 3/5] rtnetlink: do_setlink: Use sockaddr_storage

Instead of a heap allocation use a stack allocated sockaddr_storage to
support arbitrary length addr_len value (but bounds check it against the
maximum address length).

Signed-off-by: Kees Cook <kees@kernel.org>
---
  net/core/rtnetlink.c | 12 ++++--------
  1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index f0a520987085..eddd10b74f06 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c

@@ -2839,21 +2839,17 @@ static int do_setlink(const struct sk_buff *skb,
  	}
  
  	if (tb[IFLA_ADDRESS]) {
-		struct sockaddr *sa;
-		int len;
+		struct sockaddr_storage addr;
+		struct sockaddr *sa = (struct sockaddr *)&addr;

  
-		len = sizeof(sa_family_t) + max_t(size_t, dev->addr_len,
-						  sizeof(*sa));
-		sa = kmalloc(len, GFP_KERNEL);
-		if (!sa) {
+		if (dev->addr_len > sizeof(addr.__data)) {
  			err = -ENOMEM;
  			goto errout;
  		}
  		sa->sa_family = dev->type;
-		memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
+		memcpy(addr.__data, nla_data(tb[IFLA_ADDRESS]),
  		       dev->addr_len);
  		err = dev_set_mac_address_user(dev, sa, extack);
-		kfree(sa);
  		if (err)
  			goto errout;
  		status |= DO_SETLINK_MODIFIED;