On December 16, 2024 6:41:56 PM PST, Kuniyuki Iwashima <[email protected]>
wrote:
>From: Kees Cook <[email protected]>
>Date: Mon, 16 Dec 2024 18:04:45 -0800
>> 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).
>
>I remember Eric's feedback was to keep using heap instead of stack
>because rtnl_newlink() path already uses too much on stack.
See below...
>
>
>> 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).
That's why I included the rationale above. (I.e. stack usage does not grow with
this patch.)
-Kees
>>
>> Signed-off-by: Kees Cook <[email protected]>
>> ---
>> Cc: Eric Dumazet <[email protected]>
>> Cc: "David S. Miller" <[email protected]>
>> Cc: Jakub Kicinski <[email protected]>
>> Cc: Paolo Abeni <[email protected]>
>> Cc: Ido Schimmel <[email protected]>
>> Cc: Petr Machata <[email protected]>
>> Cc: [email protected]
>> ---
>> 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
>
--
Kees Cook
