BUG: KMSAN: uninit-value in selinux_socket_bind, selinux_socket_connect_helper

[Kyungtae Kim]

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 =


Thanks,
Kyungtae Kim