Date:   Thu, 6 Dec 2018 11:36:08 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     syzbot+ad5d327e6936a2e284be@...kaller.appspotmail.com
Cc:     David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>, linux-sctp@...r.kernel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Networking <netdev@...r.kernel.org>, nhorman@...driver.com,
        syzkaller-bugs@...glegroups.com,
        Vladislav Yasevich <vyasevich@...il.com>
Subject: Re: KMSAN: kernel-infoleak in sctp_getsockopt

On Wed, Dec 5, 2018 at 8:31 PM syzbot
<syzbot+ad5d327e6936a2e284be@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    fffec98ae2a6 net: proper support for CONFIG_GENERIC_CSUM o..
> git tree:       https://github.com/google/kmsan.git/master
> console output: https://syzkaller.appspot.com/x/log.txt?x=12e84a47400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=56b48b46dafe4516
> dashboard link: https://syzkaller.appspot.com/bug?extid=ad5d327e6936a2e284be
> compiler:       clang version 8.0.0 (trunk 343298)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=103cd225400000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+ad5d327e6936a2e284be@...kaller.appspotmail.com
>
> 8021q: adding VLAN 0 to HW filter on device team0
> 8021q: adding VLAN 0 to HW filter on device team0
> 8021q: adding VLAN 0 to HW filter on device team0
> 8021q: adding VLAN 0 to HW filter on device team0
> ==================================================================
> BUG: KMSAN: kernel-infoleak in _copy_to_user+0x19a/0x230 lib/usercopy.c:33
> CPU: 1 PID: 8164 Comm: syz-executor2 Not tainted 4.20.0-rc3+ #95
> 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+0x32d/0x480 lib/dump_stack.c:113
>   kmsan_report+0x12c/0x290 mm/kmsan/kmsan.c:683
>   kmsan_internal_check_memory+0x32a/0xa50 mm/kmsan/kmsan.c:743
>   kmsan_copy_to_user+0x78/0xd0 mm/kmsan/kmsan_hooks.c:634
>   _copy_to_user+0x19a/0x230 lib/usercopy.c:33
>   copy_to_user include/linux/uaccess.h:183 [inline]
>   sctp_getsockopt_local_addrs net/sctp/socket.c:5998 [inline]
>   sctp_getsockopt+0x15248/0x186f0 net/sctp/socket.c:7477
>   sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
>   __sys_getsockopt+0x489/0x550 net/socket.c:1939
>   __do_sys_getsockopt net/socket.c:1950 [inline]
>   __se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
>   __x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
>   do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
>   entry_SYSCALL_64_after_hwframe+0x63/0xe7
> RIP: 0033:0x457569
> Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f4991886c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
> RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000457569
> RDX: 000000000000006d RSI: 0000000000000084 RDI: 0000000000000003
> RBP: 000000000072bf00 R08: 0000000020000140 R09: 0000000000000000
> R10: 0000000020001100 R11: 0000000000000246 R12: 00007f49918876d4
> R13: 00000000004c7d88 R14: 00000000004ce348 R15: 00000000ffffffff
>
> Uninit was stored to memory at:
>   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
>   kmsan_save_stack mm/kmsan/kmsan.c:261 [inline]
>   kmsan_internal_chain_origin+0x13d/0x240 mm/kmsan/kmsan.c:469
>   kmsan_memcpy_memmove_metadata+0x1a9/0xf70 mm/kmsan/kmsan.c:344
>   kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:362
>   __msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:162
>   sctp_copy_laddrs net/sctp/socket.c:5901 [inline]
>   sctp_getsockopt_local_addrs net/sctp/socket.c:5967 [inline]
>   sctp_getsockopt+0x14f41/0x186f0 net/sctp/socket.c:7477
>   sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
>   __sys_getsockopt+0x489/0x550 net/socket.c:1939
>   __do_sys_getsockopt net/socket.c:1950 [inline]
>   __se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
>   __x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
>   do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
>   entry_SYSCALL_64_after_hwframe+0x63/0xe7
>
> Uninit was stored to memory at:
>   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
>   kmsan_save_stack mm/kmsan/kmsan.c:261 [inline]
>   kmsan_internal_chain_origin+0x13d/0x240 mm/kmsan/kmsan.c:469
>   kmsan_memcpy_memmove_metadata+0x1a9/0xf70 mm/kmsan/kmsan.c:344
>   kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:362
>   __msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:162
>   sctp_copy_laddrs net/sctp/socket.c:5890 [inline]
>   sctp_getsockopt_local_addrs net/sctp/socket.c:5967 [inline]
>   sctp_getsockopt+0x14de8/0x186f0 net/sctp/socket.c:7477
>   sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
>   __sys_getsockopt+0x489/0x550 net/socket.c:1939
>   __do_sys_getsockopt net/socket.c:1950 [inline]
>   __se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
>   __x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
>   do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
>   entry_SYSCALL_64_after_hwframe+0x63/0xe7
>
> Uninit was created at:
>   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
>   kmsan_internal_poison_shadow+0x6d/0x130 mm/kmsan/kmsan.c:170
>   kmsan_kmalloc+0xa1/0x100 mm/kmsan/kmsan_hooks.c:186
>   __kmalloc+0x14c/0x4d0 mm/slub.c:3825
>   kmalloc include/linux/slab.h:551 [inline]
>   sctp_inet6addr_event+0x60e/0xbd0 net/sctp/ipv6.c:100
>   notifier_call_chain kernel/notifier.c:93 [inline]
>   __atomic_notifier_call_chain kernel/notifier.c:183 [inline]
>   atomic_notifier_call_chain+0x13d/0x240 kernel/notifier.c:193
>   inet6addr_notifier_call_chain+0x76/0x90 net/ipv6/addrconf_core.c:107
>   ipv6_add_addr+0x2597/0x2890 net/ipv6/addrconf.c:1115
>   inet6_addr_add+0xc86/0x1c10 net/ipv6/addrconf.c:2912
>   inet6_rtm_newaddr+0x167e/0x3d20 net/ipv6/addrconf.c:4750
>   rtnetlink_rcv_msg+0x1148/0x1540 net/core/rtnetlink.c:4947
>   netlink_rcv_skb+0x394/0x640 net/netlink/af_netlink.c:2477
>   rtnetlink_rcv+0x50/0x60 net/core/rtnetlink.c:4965
>   netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
>   netlink_unicast+0x1699/0x1740 net/netlink/af_netlink.c:1336
>   netlink_sendmsg+0x13c7/0x1440 net/netlink/af_netlink.c:1917
>   sock_sendmsg_nosec net/socket.c:621 [inline]
>   sock_sendmsg net/socket.c:631 [inline]
>   ___sys_sendmsg+0xe3b/0x1240 net/socket.c:2116
>   __sys_sendmsg net/socket.c:2154 [inline]
>   __do_sys_sendmsg net/socket.c:2163 [inline]
>   __se_sys_sendmsg+0x305/0x460 net/socket.c:2161
>   __x64_sys_sendmsg+0x4a/0x70 net/socket.c:2161
>   do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
>   entry_SYSCALL_64_after_hwframe+0x63/0xe7
>
> Bytes 32-35 of 2100 are uninitialized
> Memory access of size 2100 starts at ffff888185d8b000
> Data copied to user address 0000000020001108
> ==================================================================
When a network device goes up and sctp_inetaddr_event() is called, it
allocates a partially initialized struct sctp_sockaddr_entry to hold
the newly created address.
The attached reproducer can be then used to read up to 8 uninit bytes
for each of the local addresses.
I guess the devices aren't created so often that this can pose any
security risk, but we probably still need to allocate this structure
with __GFP_ZERO.
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
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-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

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View attachment "dump_buf.h" of type "text/x-chdr" (1701 bytes)

View attachment "getsockopt.c" of type "text/x-csrc" (1168 bytes)

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