Re: [PATCH net] sctp: initialize _pad of sockaddr_in before copying to user memory

[David Miller <davem@davemloft.net>]

From: Xin Long <lucien.xin@gmail.com>
Date: Sun, 31 Mar 2019 16:58:15 +0800

> 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@syzkaller.appspotmail.com
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied and queued up for -stable, thanks Xin!