KMSAN: uninit-value in strcmp

KMSAN: uninit-value in strcmp

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    d2d741e5d189 kmsan: add initialization for shmem pages
git tree:       https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=10051497800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=48f9de3384bcd0f
dashboard link: https://syzkaller.appspot.com/bug?extid=df0257c92ffd4fcc58cd
compiler:       clang version 7.0.0 (trunk 329391)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=11275657800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17c3d5e7800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+df0257c92ffd4fcc58cd@syzkaller.appspotmail.com

==================================================================
BUG: KMSAN: uninit-value in strcmp+0xf7/0x160 lib/string.c:329
CPU: 1 PID: 4527 Comm: syz-executor655 Not tainted 4.16.0+ #87
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x185/0x1d0 lib/dump_stack.c:53
  kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
  __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683
  strcmp+0xf7/0x160 lib/string.c:329
  tipc_nl_node_get_link+0x220/0x6f0 net/tipc/node.c:1881
  genl_family_rcv_msg net/netlink/genetlink.c:599 [inline]
  genl_rcv_msg+0x1686/0x1810 net/netlink/genetlink.c:624
  netlink_rcv_skb+0x378/0x600 net/netlink/af_netlink.c:2447
  genl_rcv+0x63/0x80 net/netlink/genetlink.c:635
  netlink_unicast_kernel net/netlink/af_netlink.c:1311 [inline]
  netlink_unicast+0x166b/0x1740 net/netlink/af_netlink.c:1337
  netlink_sendmsg+0x1048/0x1310 net/netlink/af_netlink.c:1900
  sock_sendmsg_nosec net/socket.c:630 [inline]
  sock_sendmsg net/socket.c:640 [inline]
  ___sys_sendmsg+0xec0/0x1310 net/socket.c:2046
  __sys_sendmsg net/socket.c:2080 [inline]
  SYSC_sendmsg+0x2a3/0x3d0 net/socket.c:2091
  SyS_sendmsg+0x54/0x80 net/socket.c:2087
  do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
RIP: 0033:0x445589
RSP: 002b:00007fb7ee66cdb8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000006dac24 RCX: 0000000000445589
RDX: 0000000000000000 RSI: 0000000020023000 RDI: 0000000000000003
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fffa2bf3f3f R14: 00007fb7ee66d9c0 R15: 0000000000000001

Uninit was created at:
  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:278 [inline]
  kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:188
  kmsan_kmalloc+0x94/0x100 mm/kmsan/kmsan.c:314
  kmsan_slab_alloc+0x11/0x20 mm/kmsan/kmsan.c:321
  slab_post_alloc_hook mm/slab.h:445 [inline]
  slab_alloc_node mm/slub.c:2737 [inline]
  __kmalloc_node_track_caller+0xaed/0x11c0 mm/slub.c:4369
  __kmalloc_reserve net/core/skbuff.c:138 [inline]
  __alloc_skb+0x2cf/0x9f0 net/core/skbuff.c:206
  alloc_skb include/linux/skbuff.h:984 [inline]
  netlink_alloc_large_skb net/netlink/af_netlink.c:1183 [inline]
  netlink_sendmsg+0x9a6/0x1310 net/netlink/af_netlink.c:1875
  sock_sendmsg_nosec net/socket.c:630 [inline]
  sock_sendmsg net/socket.c:640 [inline]
  ___sys_sendmsg+0xec0/0x1310 net/socket.c:2046
  __sys_sendmsg net/socket.c:2080 [inline]
  SYSC_sendmsg+0x2a3/0x3d0 net/socket.c:2091
  SyS_sendmsg+0x54/0x80 net/socket.c:2087
  do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
==================================================================


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Re: KMSAN: uninit-value in strcmp

[David Miller]

From: syzbot <syzbot+df0257c92ffd4fcc58cd@syzkaller.appspotmail.com>
Date: Thu, 03 May 2018 11:44:02 -0700

> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x185/0x1d0 lib/dump_stack.c:53
>  kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
>  __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683
>  strcmp+0xf7/0x160 lib/string.c:329
>  tipc_nl_node_get_link+0x220/0x6f0 net/tipc/node.c:1881
>  genl_family_rcv_msg net/netlink/genetlink.c:599 [inline]

Hmmm, TIPC_NL_LINK_GET uses tipc_nl_policy, which has a proper nesting
entry for TIPC_NLA_LINK.  I wonder how the code goes about validating
TIPC_NLA_LINK_NAME in such a case?  Does it?

This may be the problem.

RE: KMSAN: uninit-value in strcmp

[Jon Maloy]

> -----Original Message-----
> From: David Miller [mailto:davem@davemloft.net]
> Sent: Thursday, May 03, 2018 15:22
> To: syzbot+df0257c92ffd4fcc58cd@syzkaller.appspotmail.com
> Cc: Jon Maloy <jon.maloy@ericsson.com>; linux-kernel@vger.kernel.org;
> netdev@vger.kernel.org; syzkaller-bugs@googlegroups.com; tipc-
> discussion@lists.sourceforge.net; ying.xue@windriver.com
> Subject: Re: KMSAN: uninit-value in strcmp
> 
> From: syzbot <syzbot+df0257c92ffd4fcc58cd@syzkaller.appspotmail.com>
> Date: Thu, 03 May 2018 11:44:02 -0700
> 
> > Call Trace:
> >  __dump_stack lib/dump_stack.c:17 [inline]
> >  dump_stack+0x185/0x1d0 lib/dump_stack.c:53
> >  kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
> >  __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683
> >  strcmp+0xf7/0x160 lib/string.c:329
> >  tipc_nl_node_get_link+0x220/0x6f0 net/tipc/node.c:1881
> > genl_family_rcv_msg net/netlink/genetlink.c:599 [inline]
> 
> Hmmm, TIPC_NL_LINK_GET uses tipc_nl_policy, which has a proper nesting
> entry for TIPC_NLA_LINK.  I wonder how the code goes about validating
> TIPC_NLA_LINK_NAME in such a case?  Does it?

I assume that a strncmp() instead of a strcmp() would avert this particular crash, but it doesn't sound like that is what you are after here?
To be honest, I will need to study this code a little myself to understand if there is more that has to be done.

///jon

> 
> This may be the problem.

Re: KMSAN: uninit-value in strcmp

[Ying Xue]

On 05/04/2018 03:22 AM, David Miller wrote:
> From: syzbot <syzbot+df0257c92ffd4fcc58cd@syzkaller.appspotmail.com>
> Date: Thu, 03 May 2018 11:44:02 -0700
> 
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:17 [inline]
>>  dump_stack+0x185/0x1d0 lib/dump_stack.c:53
>>  kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
>>  __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683
>>  strcmp+0xf7/0x160 lib/string.c:329
>>  tipc_nl_node_get_link+0x220/0x6f0 net/tipc/node.c:1881
>>  genl_family_rcv_msg net/netlink/genetlink.c:599 [inline]
> 
> Hmmm, TIPC_NL_LINK_GET uses tipc_nl_policy, which has a proper nesting
> entry for TIPC_NLA_LINK.  I wonder how the code goes about validating
> TIPC_NLA_LINK_NAME in such a case?  Does it?
> 
> This may be the problem.

David, you are right. This is absolutely a real bug. As you said, we
didn't validate TIPC_NLA_LINK_NAME attribute in tipc_nl_node_get_link()
at all.

I will submit a patch to fix the issue soon.

> 

Re: KMSAN: uninit-value in strcmp

[Ying Xue]

On 05/04/2018 03:22 AM, David Miller wrote:
> From: syzbot <syzbot+df0257c92ffd4fcc58cd@syzkaller.appspotmail.com>
> Date: Thu, 03 May 2018 11:44:02 -0700
> 
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:17 [inline]
>>  dump_stack+0x185/0x1d0 lib/dump_stack.c:53
>>  kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
>>  __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683
>>  strcmp+0xf7/0x160 lib/string.c:329
>>  tipc_nl_node_get_link+0x220/0x6f0 net/tipc/node.c:1881
>>  genl_family_rcv_msg net/netlink/genetlink.c:599 [inline]
> 
> Hmmm, TIPC_NL_LINK_GET uses tipc_nl_policy, which has a proper nesting
> entry for TIPC_NLA_LINK.  I wonder how the code goes about validating
> TIPC_NLA_LINK_NAME in such a case?  Does it?
> 
> This may be the problem.

David, you are right. This is absolutely a real bug. As you said, we
didn't validate TIPC_NLA_LINK_NAME attribute in tipc_nl_node_get_link()
at all.

I will submit a patch to fix the issue soon.

> 

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