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Date:   Mon, 1 Apr 2019 10:43:55 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        David Miller <davem@...emloft.net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] sctp: initialize _pad of sockaddr_in before copying
 to user memory

On Sun, Mar 31, 2019 at 10:58 AM Xin Long <lucien.xin@...il.com> wrote:
>
> Syzbot report a kernel-infoleak:
>
>   BUG: KMSAN: kernel-infoleak in _copy_to_user+0x16b/0x1f0 lib/usercopy.c:32
>   Call Trace:
>     _copy_to_user+0x16b/0x1f0 lib/usercopy.c:32
>     copy_to_user include/linux/uaccess.h:174 [inline]
>     sctp_getsockopt_peer_addrs net/sctp/socket.c:5911 [inline]
>     sctp_getsockopt+0x1668e/0x17f70 net/sctp/socket.c:7562
>     ...
>   Uninit was stored to memory at:
>     sctp_transport_init net/sctp/transport.c:61 [inline]
>     sctp_transport_new+0x16d/0x9a0 net/sctp/transport.c:115
>     sctp_assoc_add_peer+0x532/0x1f70 net/sctp/associola.c:637
>     sctp_process_param net/sctp/sm_make_chunk.c:2548 [inline]
>     sctp_process_init+0x1a1b/0x3ed0 net/sctp/sm_make_chunk.c:2361
>     ...
>   Bytes 8-15 of 16 are uninitialized
>
> It was caused by that th _pad field (the 8-15 bytes) of a v4 addr (saved in
> struct sockaddr_in) wasn't initialized, but directly copied to user memory
> in sctp_getsockopt_peer_addrs().
>
> So fix it by calling memset(addr->v4.sin_zero, 0, 8) to initialize _pad of
> sockaddr_in before copying it to user memory in sctp_v4_addr_to_user(), as
> sctp_v6_addr_to_user() does.
>
> Reported-by: syzbot+86b5c7c236a22616a72f@...kaller.appspotmail.com
> Signed-off-by: Xin Long <lucien.xin@...il.com>
Tested-by: Alexander Potapenko <glider@...gle.com>
> ---
>  net/sctp/protocol.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
> index 6abc8b2..951afde 100644
> --- a/net/sctp/protocol.c
> +++ b/net/sctp/protocol.c
> @@ -600,6 +600,7 @@ static struct sock *sctp_v4_create_accept_sk(struct sock *sk,
>  static int sctp_v4_addr_to_user(struct sctp_sock *sp, union sctp_addr *addr)
>  {
>         /* No address mapping for V4 sockets */
> +       memset(addr->v4.sin_zero, 0, sizeof(addr->v4.sin_zero));
>         return sizeof(struct sockaddr_in);
>  }
>
> --
> 2.1.0
>
> --
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-- 
Alexander Potapenko
Software Engineer

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