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Date:   Fri, 29 Mar 2019 14:30:39 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     syzbot <syzbot+86b5c7c236a22616a72f@...kaller.appspotmail.com>,
        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>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Vladislav Yasevich <vyasevich@...il.com>
Subject: Re: KMSAN: kernel-infoleak in sctp_getsockopt (3)

On Fri, Mar 29, 2019 at 06:35:40PM +0100, Alexander Potapenko wrote:
> On Fri, Mar 29, 2019 at 3:51 PM Neil Horman <nhorman@...driver.com> wrote:
> >
> > On Thu, Mar 28, 2019 at 09:25:06AM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following crash on:
> > >
> > > HEAD commit:    c10a026b kmsan: use __free_pages() in kmsan_iounmap_page_r..
> > > git tree:       kmsan
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=107d3c7d200000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=a5675814e8eae69e
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=86b5c7c236a22616a72f
> > > compiler:       clang version 8.0.0 (trunk 350509)
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1252834d200000
> > >
> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: syzbot+86b5c7c236a22616a72f@...kaller.appspotmail.com
> > >
> > > IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_hsr: link becomes ready
> > > IPv6: ADDRCONF(NETDEV_CHANGE): hsr_slave_1: link becomes ready
> > > 8021q: adding VLAN 0 to HW filter on device batadv0
> > > 8021q: adding VLAN 0 to HW filter on device batadv0
> > > ==================================================================
> > > BUG: KMSAN: kernel-infoleak in _copy_to_user+0x16b/0x1f0 lib/usercopy.c:32
> > > CPU: 0 PID: 10131 Comm: syz-executor.4 Not tainted 5.0.0+ #16
> > > 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+0x173/0x1d0 lib/dump_stack.c:113
> > >  kmsan_report+0x131/0x2a0 mm/kmsan/kmsan.c:636
> > >  kmsan_internal_check_memory+0xaa1/0xbb0 mm/kmsan/kmsan.c:730
> > >  kmsan_copy_to_user+0xab/0xc0 mm/kmsan/kmsan_hooks.c:485
> > >  _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
> > >  sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2950
> > >  __sys_getsockopt+0x489/0x550 net/socket.c:1938
> > >  __do_sys_getsockopt net/socket.c:1949 [inline]
> > >  __se_sys_getsockopt+0xe1/0x100 net/socket.c:1946
> > >  __x64_sys_getsockopt+0x62/0x80 net/socket.c:1946
> > >  do_syscall_64+0xbc/0xf0 arch/x86/entry/common.c:291
> > >  entry_SYSCALL_64_after_hwframe+0x63/0xe7
> > > RIP: 0033:0x458209
> > > Code: ad b8 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 7b b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> > > RSP: 002b:00007fdbef191c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
> > > RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000458209
> > > RDX: 000000000000006c RSI: 0000000000000084 RDI: 0000000000000004
> > > RBP: 000000000073bf00 R08: 0000000020000300 R09: 0000000000000000
> > > R10: 0000000020000280 R11: 0000000000000246 R12: 00007fdbef1926d4
> > > R13: 00000000004c96c8 R14: 00000000004d0310 R15: 00000000ffffffff
> > >
> > > Uninit was stored to memory at:
> > >  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:205 [inline]
> > >  kmsan_save_stack mm/kmsan/kmsan.c:220 [inline]
> > >  kmsan_internal_chain_origin+0x134/0x230 mm/kmsan/kmsan.c:426
> > >  kmsan_memcpy_memmove_metadata+0xb5b/0xfe0 mm/kmsan/kmsan.c:304
> > >  kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:324
> > >  __msan_memcpy+0x58/0x70 mm/kmsan/kmsan_instr.c:139
> > >  sctp_getsockopt_peer_addrs net/sctp/socket.c:5906 [inline]
> > >  sctp_getsockopt+0x16556/0x17f70 net/sctp/socket.c:7562
> > >  sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2950
> > >  __sys_getsockopt+0x489/0x550 net/socket.c:1938
> > >  __do_sys_getsockopt net/socket.c:1949 [inline]
> > >  __se_sys_getsockopt+0xe1/0x100 net/socket.c:1946
> > >  __x64_sys_getsockopt+0x62/0x80 net/socket.c:1946
> > >  do_syscall_64+0xbc/0xf0 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:205 [inline]
> > >  kmsan_save_stack mm/kmsan/kmsan.c:220 [inline]
> > >  kmsan_internal_chain_origin+0x134/0x230 mm/kmsan/kmsan.c:426
> > >  kmsan_memcpy_memmove_metadata+0xb5b/0xfe0 mm/kmsan/kmsan.c:304
> > >  kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:324
> > >  __msan_memcpy+0x58/0x70 mm/kmsan/kmsan_instr.c:139
> > >  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
> > >  sctp_cmd_process_init net/sctp/sm_sideeffect.c:682 [inline]
> > >  sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1410 [inline]
> > >  sctp_side_effects net/sctp/sm_sideeffect.c:1220 [inline]
> > >  sctp_do_sm+0x3cfc/0x9af0 net/sctp/sm_sideeffect.c:1191
> > >  sctp_assoc_bh_rcv+0x65a/0xd80 net/sctp/associola.c:1074
> > >  sctp_inq_push+0x300/0x420 net/sctp/inqueue.c:95
> > >  sctp_backlog_rcv+0x20a/0xaf0 net/sctp/input.c:354
> > >  sk_backlog_rcv include/net/sock.h:936 [inline]
> > >  __release_sock+0x281/0x5f0 net/core/sock.c:2284
> > >  release_sock+0x99/0x2a0 net/core/sock.c:2800
> > >  sctp_wait_for_connect+0x3ee/0x860 net/sctp/socket.c:8751
> > >  sctp_sendmsg_to_asoc+0x2167/0x21a0 net/sctp/socket.c:1967
> > >  sctp_sendmsg+0x3fd7/0x6700 net/sctp/socket.c:2113
> > >  inet_sendmsg+0x54a/0x720 net/ipv4/af_inet.c:798
> > >  sock_sendmsg_nosec net/socket.c:622 [inline]
> > >  sock_sendmsg net/socket.c:632 [inline]
> > >  ___sys_sendmsg+0xdb9/0x11b0 net/socket.c:2115
> > >  __sys_sendmsg net/socket.c:2153 [inline]
> > >  __do_sys_sendmsg net/socket.c:2162 [inline]
> > >  __se_sys_sendmsg+0x305/0x460 net/socket.c:2160
> > >  __x64_sys_sendmsg+0x4a/0x70 net/socket.c:2160
> > >  do_syscall_64+0xbc/0xf0 arch/x86/entry/common.c:291
> > >  entry_SYSCALL_64_after_hwframe+0x63/0xe7
> > >
> > > Local variable description: ----addr.i@...p_process_init
> > > Variable was created at:
> > >  sctp_process_init+0xb5/0x3ed0 net/sctp/sm_make_chunk.c:2324
> > >  sctp_cmd_process_init net/sctp/sm_sideeffect.c:682 [inline]
> > >  sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1410 [inline]
> > >  sctp_side_effects net/sctp/sm_sideeffect.c:1220 [inline]
> > >  sctp_do_sm+0x3cfc/0x9af0 net/sctp/sm_sideeffect.c:1191
> > >
> > > Bytes 8-15 of 16 are uninitialized
> > > Memory access of size 16 starts at ffff88809511fc28
> > > Data copied to user address 0000000020000298
> > > ==================================================================
> > >
> > >
> > > ---
> > > 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#status for how to communicate with syzbot.
> > > syzbot can test patches for this bug, for details see:
> > > https://goo.gl/tpsmEJ#testing-patches
> > >
> > >
> >
> >
> > Hmm, odd.  I see where we are doing the copy_to_user call in
> > getsockopt_peer_addrs, but the length we copy should always be equal to or less
> > than what was memcopied to the temp variable.  False positive?
> I'll take a closer look next week.
> The bug is reproducible with the following syzkaller program:
> 
> r0 = socket$inet(0x2, 0x80001, 0x84)
> bind$inet(r0, &(0x7f0000000080)={0x2, 0x4e20, @empty}, 0x10)
> sendmsg(r0, &(0x7f0000000100)={&(0x7f0000006000)=@...{0x2, 0x4e20,
> @loopback}, 0x80, &(0x7f0000007f80)=[{&(0x7f00000001c0)="de", 0x1}],
> 0x1}, 0x0)
> getsockopt$inet_sctp_SCTP_GET_PEER_ADDRS(r0, 0x84, 0x6c,
> &(0x7f0000000000)={<r5=>0x0, 0x38,
> "41925f90e4121fadc9c1296dd22ae19d0b1b0942e46fc79e2ecec1056b23199f0ca008915d8dba1b3896c154f2244bbe859fe3423a4b437a"},
> &(0x7f0000000040)=0x40)
> 
> Just need to check where the uninitializedness comes from.
my only guess would be if we somehow copied an ipv4 address worth of data to the
buffer (which contains an enum for both ipv4 and ipv6 addresses), and then
copied an ipv6 address worth of data to userspace, but I don't yet see how that
can happen.

Neil

> > Neil
> >
> 
> 
> 
> --
> Alexander Potapenko
> Software Engineer
> 
> Google Germany GmbH
> Erika-Mann-Straße, 33
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> 
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