From: Kees Cook <k...@kernel.org>
Date: Mon, 16 Dec 2024 23:53:46 -0800
> On December 16, 2024 6:41:56 PM PST, Kuniyuki Iwashima <kun...@amazon.com>
> wrote:
> >From: Kees Cook <k...@kernel.org>
> >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.)
Ah okay, but I think we can't cap the address size to 14
bytes. MAX_ADDR_LEN is 32.
Also, dev_set_mac_address_user() still uses dev->addr_len.
>
> -Kees
>
> >>
> >> Signed-off-by: Kees Cook <k...@kernel.org>
> >> ---
> >> Cc: Eric Dumazet <eduma...@google.com>
> >> Cc: "David S. Miller" <da...@davemloft.net>
> >> Cc: Jakub Kicinski <k...@kernel.org>
> >> Cc: Paolo Abeni <pab...@redhat.com>
> >> Cc: Ido Schimmel <ido...@nvidia.com>
> >> Cc: Petr Machata <pe...@nvidia.com>
> >> Cc: net...@vger.kernel.org
> >> ---
> >> 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
