linux-kernel - Re: [PATCH] rtnetlink: do_setlink: Use true struct sockaddr

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Message-ID: <980CE89E-0E8A-4A0D-A1E4-D03DB8F86A21@kernel.org>
Date: Tue, 17 Dec 2024 01:33:33 -0800
From: Kees Cook <kees@...nel.org>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
CC: davem@...emloft.net, edumazet@...gle.com, horms@...nel.org, idosch@...dia.com,
 kuba@...nel.org, kuniyu@...zon.com, linux-hardening@...r.kernel.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org, pabeni@...hat.com,
 petrm@...dia.com
Subject: Re: [PATCH] rtnetlink: do_setlink: Use true struct sockaddr



On December 17, 2024 12:03:35 AM PST, Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>From: Kees Cook <kees@...nel.org>
>Date: Mon, 16 Dec 2024 23:53:46 -0800
>> On December 16, 2024 6:41:56 PM PST, Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>> >From: Kees Cook <kees@...nel.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.

Oh, hrm, yes, that's true. I had audited callers of dev_set_mac_address(), but I think I must have missed callers of dev_set_mac_address_user(). Ugh. :( Let me take another look at this...

-Kees

>
>
>> 
>> -Kees
>> 
>> >> 
>> >> Signed-off-by: Kees Cook <kees@...nel.org>
>> >> ---
>> >> Cc: Eric Dumazet <edumazet@...gle.com>
>> >> Cc: "David S. Miller" <davem@...emloft.net>
>> >> Cc: Jakub Kicinski <kuba@...nel.org>
>> >> Cc: Paolo Abeni <pabeni@...hat.com>
>> >> Cc: Ido Schimmel <idosch@...dia.com>
>> >> Cc: Petr Machata <petrm@...dia.com>
>> >> Cc: netdev@...r.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

-- 
Kees Cook