linux-kernel - Re: [PATCH] net: don't call strlen() on the user buffer in packet_bind

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Date:   Tue, 28 Feb 2017 14:47:37 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Dmitriy Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: don't call strlen() on the user buffer in packet_bind_spkt()

On Tue, Feb 28, 2017 at 2:42 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Tue, 2017-02-28 at 05:33 -0800, Eric Dumazet wrote:
>
>> It looks a bug in this implementation of strlcpy() then.
>>
>
> Apparently strlcpy(dest, src, size)  returns strlen(src), so we can not
> use it in this context.
Good point.
>> sizeof(name) is 15.
>>
>> If you use strncpy(X, uaddr->sa_data, 15) , then you might access
>> uaddr->sa_data[14] and this would still be wrong, since sa_data has 14
>> bytes only :
>>
>>
>> struct sockaddr {
>>   sa_family_t sa_family;
>>   char        sa_data[14];
>> };
>
>
> Maybe then :
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 2bd0d1949312c3d71c4b33529316dcfe76fa28f1..d2e7caa79d2604363316c7316864bed1f4971d29 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -3103,7 +3103,7 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr,
>                             int addr_len)
>  {
>         struct sock *sk = sock->sk;
> -       char name[15];
> +       char name[sizeof(uaddr->sa_data) + 1];
>
>         /*
>          *      Check legality
> @@ -3111,7 +3111,8 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr,
>
>         if (addr_len != sizeof(struct sockaddr))
>                 return -EINVAL;
> -       strlcpy(name, uaddr->sa_data, sizeof(name));
> +       memcpy(name, uaddr->sa_data, sizeof(uaddr->sa_data));
> +       name[sizeof(uaddr->sa_data)] = 0;
>
>         return packet_do_bind(sk, name, 0, pkt_sk(sk)->num);
>  }
>
SGTM. Shall I send the updated patch? (Sorry for asking, the patch
culture is hard)
>



-- 
Alexander Potapenko
Software Engineer

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