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

[Eric Dumazet]

On 11/4/24 11:25 PM, Kees Cook wrote:

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 <k...@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;

We already use too much stack space.


Please move addr into struct rtnl_newlink_tbs ?

- 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;