netdev - Re: [PATCH net] xfrm_user: prevent leaking 2 bytes of kernel memory

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Message-ID: <20180619125935.7yljuoqmd64ljye4@gauss3.secunet.de>
Date:   Tue, 19 Jun 2018 14:59:35 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Eric Dumazet <edumazet@...gle.com>
CC:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH net] xfrm_user: prevent leaking 2 bytes of kernel memory

On Mon, Jun 18, 2018 at 09:35:07PM -0700, Eric Dumazet wrote:
> struct xfrm_userpolicy_type has two holes, so we should not
> use C99 style initializer.
> 
> KMSAN report:
> 
> BUG: KMSAN: kernel-infoleak in copyout lib/iov_iter.c:140 [inline]
> BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x1b14/0x2800 lib/iov_iter.c:571
> CPU: 1 PID: 4520 Comm: syz-executor841 Not tainted 4.17.0+ #5
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x185/0x1d0 lib/dump_stack.c:113
>  kmsan_report+0x188/0x2a0 mm/kmsan/kmsan.c:1117
>  kmsan_internal_check_memory+0x138/0x1f0 mm/kmsan/kmsan.c:1211
>  kmsan_copy_to_user+0x7a/0x160 mm/kmsan/kmsan.c:1253
>  copyout lib/iov_iter.c:140 [inline]
>  _copy_to_iter+0x1b14/0x2800 lib/iov_iter.c:571
>  copy_to_iter include/linux/uio.h:106 [inline]
>  skb_copy_datagram_iter+0x422/0xfa0 net/core/datagram.c:431
>  skb_copy_datagram_msg include/linux/skbuff.h:3268 [inline]
>  netlink_recvmsg+0x6f1/0x1900 net/netlink/af_netlink.c:1959
>  sock_recvmsg_nosec net/socket.c:802 [inline]
>  sock_recvmsg+0x1d6/0x230 net/socket.c:809
>  ___sys_recvmsg+0x3fe/0x810 net/socket.c:2279
>  __sys_recvmmsg+0x58e/0xe30 net/socket.c:2391
>  do_sys_recvmmsg+0x2a6/0x3e0 net/socket.c:2472
>  __do_sys_recvmmsg net/socket.c:2485 [inline]
>  __se_sys_recvmmsg net/socket.c:2481 [inline]
>  __x64_sys_recvmmsg+0x15d/0x1c0 net/socket.c:2481
>  do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x446ce9
> RSP: 002b:00007fc307918db8 EFLAGS: 00000293 ORIG_RAX: 000000000000012b
> RAX: ffffffffffffffda RBX: 00000000006dbc24 RCX: 0000000000446ce9
> RDX: 000000000000000a RSI: 0000000020005040 RDI: 0000000000000003
> RBP: 00000000006dbc20 R08: 0000000020004e40 R09: 0000000000000000
> R10: 0000000040000000 R11: 0000000000000293 R12: 0000000000000000
> R13: 00007ffc8d2df32f R14: 00007fc3079199c0 R15: 0000000000000001
> 
> Uninit was stored to memory at:
>  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:279 [inline]
>  kmsan_save_stack mm/kmsan/kmsan.c:294 [inline]
>  kmsan_internal_chain_origin+0x12b/0x210 mm/kmsan/kmsan.c:685
>  kmsan_memcpy_origins+0x11d/0x170 mm/kmsan/kmsan.c:527
>  __msan_memcpy+0x109/0x160 mm/kmsan/kmsan_instr.c:413
>  __nla_put lib/nlattr.c:569 [inline]
>  nla_put+0x276/0x340 lib/nlattr.c:627
>  copy_to_user_policy_type net/xfrm/xfrm_user.c:1678 [inline]
>  dump_one_policy+0xbe1/0x1090 net/xfrm/xfrm_user.c:1708
>  xfrm_policy_walk+0x45a/0xd00 net/xfrm/xfrm_policy.c:1013
>  xfrm_dump_policy+0x1c0/0x2a0 net/xfrm/xfrm_user.c:1749
>  netlink_dump+0x9b5/0x1550 net/netlink/af_netlink.c:2226
>  __netlink_dump_start+0x1131/0x1270 net/netlink/af_netlink.c:2323
>  netlink_dump_start include/linux/netlink.h:214 [inline]
>  xfrm_user_rcv_msg+0x8a3/0x9b0 net/xfrm/xfrm_user.c:2577
>  netlink_rcv_skb+0x37e/0x600 net/netlink/af_netlink.c:2448
>  xfrm_netlink_rcv+0xb2/0xf0 net/xfrm/xfrm_user.c:2598
>  netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
>  netlink_unicast+0x1680/0x1750 net/netlink/af_netlink.c:1336
>  netlink_sendmsg+0x104f/0x1350 net/netlink/af_netlink.c:1901
>  sock_sendmsg_nosec net/socket.c:629 [inline]
>  sock_sendmsg net/socket.c:639 [inline]
>  ___sys_sendmsg+0xec8/0x1320 net/socket.c:2117
>  __sys_sendmsg net/socket.c:2155 [inline]
>  __do_sys_sendmsg net/socket.c:2164 [inline]
>  __se_sys_sendmsg net/socket.c:2162 [inline]
>  __x64_sys_sendmsg+0x331/0x460 net/socket.c:2162
>  do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> Local variable description: ----upt.i@...p_one_policy
> Variable was created at:
>  dump_one_policy+0x78/0x1090 net/xfrm/xfrm_user.c:1689
>  xfrm_policy_walk+0x45a/0xd00 net/xfrm/xfrm_policy.c:1013
> 
> Byte 130 of 137 is uninitialized
> Memory access starts at ffff88019550407f
> 
> Fixes: c0144beaeca42 ("[XFRM] netlink: Use nla_put()/NLA_PUT() variantes")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Cc: Steffen Klassert <steffen.klassert@...unet.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> ---
>  net/xfrm/xfrm_user.c | 8 +++++---

It is a fix for xfrm, so I applied it
to the ipsec tree.

Thanks a lot Eric!