Re: BUG: KMSAN: uninit-value in selinux_socket_bind, selinux_socket_connect_helper

[Alexander Potapenko]

On Thu, Oct 25, 2018 at 12:35 PM Kyungtae Kim <kt0755@xxxxxxxxx> wrote:
>
> We report two crashes related (in v4.19-rc8) :
> "BUG: KMSAN: uninit-value in selinux_socket_bind"
> "BUG: KMSAN: uninit-value in selinux_socket_connect_helperâ
>
> kernel config: https://kt0755.github.io/etc/config-4.19-rc2.kmsan
> repro: https://kt0755.github.io/etc/repro.b0e55.c
>
> Since both crashes share the same issue, we just explain one of the two.
> When the third argument of bind() (i.e., addrlen) is zero, in __sys_bind(),
> data copy from user sockaddr to kernel sockaddr does not occur
> (net/socket.c:186).
> However, a subsequent function selinux_socket_bind() tries to read
> the kernel sockaddr (address->sa_family) that was not initialized at all.
>
> Crash log1
> ==================================================================
> BUG: KMSAN: uninit-value in selinux_socket_bind+0x61b/0x1040
> security/selinux/hooks.c:4643
> CPU: 0 PID: 19070 Comm: syz-executor6 Not tainted 4.19.0-rc8+ #18
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x305/0x460 lib/dump_stack.c:113
>  kmsan_report+0x1a2/0x2e0 mm/kmsan/kmsan.c:917
>  __msan_warning+0x7d/0xe0 mm/kmsan/kmsan_instr.c:500
>  selinux_socket_bind+0x61b/0x1040 security/selinux/hooks.c:4643
>  security_socket_bind+0x127/0x200 security/security.c:1390
>  __sys_bind+0x577/0x7e0 net/socket.c:1479
>  __do_sys_bind net/socket.c:1494 [inline]
>  __se_sys_bind+0x8d/0xb0 net/socket.c:1492
>  __x64_sys_bind+0x4a/0x70 net/socket.c:1492
>  do_syscall_64+0xb8/0x100 arch/x86/entry/common.c:291
>  entry_SYSCALL_64_after_hwframe+0x63/0xe7
> RIP: 0033:0x4497b9
> Code: e8 8c 9f 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 9b 6b fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fdddf1e9c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
> RAX: ffffffffffffffda RBX: 00007fdddf1ea6cc RCX: 00000000004497b9
> RDX: 0000000000000000 RSI: 0000000020000040 RDI: 0000000000000013
> RBP: 000000000071bea0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000000004c8 R14: 00000000006e8568 R15: 00007fdddf1ea700
>
> Local variable description: ----address@__sys_bind
> Variable was created at:
>  __sys_bind+0x89/0x7e0 net/socket.c:1470
>  __do_sys_bind net/socket.c:1494 [inline]
>  __se_sys_bind+0x8d/0xb0 net/socket.c:1492
> ==================================================================
>
> Crash log2
> ==================================================================
> BUG: KMSAN: uninit-value in selinux_socket_connect_helper+0x55c/0x960
> security/selinux/hooks.c:4775
> CPU: 0 PID: 8234 Comm: syz-executor2 Not tainted 4.19.0-rc8+ #18
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x305/0x460 lib/dump_stack.c:113
>  kmsan_report+0x1a2/0x2e0 mm/kmsan/kmsan.c:917
>  __msan_warning+0x7d/0xe0 mm/kmsan/kmsan_instr.c:500
>  selinux_socket_connect_helper+0x55c/0x960 security/selinux/hooks.c:4775
>  selinux_socket_connect+0xbe/0x180 security/selinux/hooks.c:4834
>  security_socket_connect+0x127/0x200 security/security.c:1395
>  __sys_connect+0x577/0x850 net/socket.c:1660
>  __do_sys_connect net/socket.c:1675 [inline]
>  __se_sys_connect+0x8d/0xb0 net/socket.c:1672
>  __x64_sys_connect+0x4a/0x70 net/socket.c:1672
>  do_syscall_64+0xb8/0x100 arch/x86/entry/common.c:291
>  entry_SYSCALL_64_after_hwframe+0x63/0xe7
> RIP: 0033:0x4497b9
> Code: e8 8c 9f 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 9b 6b fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ff660d67c68 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
> RAX: ffffffffffffffda RBX: 00007ff660d686cc RCX: 00000000004497b9
> RDX: 0000000000000000 RSI: 0000000020000000 RDI: 0000000000000013
> RBP: 000000000071bea0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 0000000000000ae0 R14: 00000000006e8b80 R15: 00007ff660d68700
>
> Local variable description: ----address@__sys_connect
> Variable was created at:
>  __sys_connect+0x89/0x850 net/socket.c:1647
>  __do_sys_connect net/socket.c:1675 [inline]
>  __se_sys_connect+0x8d/0xb0 net/socket.c:1672
> ==================================================================
>
> We provide a simple patch below to stop them.
> There are a few more lines that invoke move_addr_to_kernel(), but the
> two of them
> (bind and connect) seem to be the only cases to be corrected.
>
>
> diff --git a/net/socket.c b/net/socket.c
> index 390a8ec..de0931c2 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -1475,7 +1475,7 @@ int __sys_bind(int fd, struct sockaddr __user
> *umyaddr, int addrlen)
>         sock = sockfd_lookup_light(fd, &err, &fput_needed);
>         if (sock) {
>                 err = move_addr_to_kernel(umyaddr, addrlen, &address);
> -               if (err >= 0) {
> +               if (err > 0) {
>                         err = security_socket_bind(sock,
>                                                    (struct sockaddr *)&address,
>                                                    addrlen);
> @@ -1653,7 +1653,7 @@ int __sys_connect(int fd, struct sockaddr __user
> *uservaddr, int addrlen)
>         if (!sock)
>                 goto out;
>         err = move_addr_to_kernel(uservaddr, addrlen, &address);
> -       if (err < 0)
> +       if (err <= 0)
>                 goto out_put;
>
>         err =
I believe a better fix would be to add an |addrlen| check to
selinux_socket_bind(), which is illegally assuming
|address->sa_family| contains any reasonable data regardless of actual
address length.
I suspect the bug has been introduced in
https://github.com/torvalds/linux/commit/0f8db8cc73df60b3de9a5eebd8f117b56eff5b03
>
> Thanks,
> Kyungtae Kim
>
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-- 
Alexander Potapenko
Software Engineer

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