[PATCH] general protection fault in sock_has_perm

[Mark Salyzyn]

general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 14233 Comm: syz-executor2 Not tainted 4.4.112-g5f6325b #28
task: ffff8801d1095f00 task.stack: ffff8800b5950000
RIP: 0010:[<ffffffff81b69b7e>]  [<ffffffff81b69b7e>] sock_has_perm+0x1fe/0x3e0 security/selinux/hooks.c:4069
RSP: 0018:ffff8800b5957ce0  EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 1ffff10016b2af9f RCX: ffffffff81b69b51
RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000010
RBP: ffff8800b5957de0 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff10016b2af68 R12: ffff8800b5957db8
R13: 0000000000000000 R14: ffff8800b7259f40 R15: 00000000000000d7
FS:  00007f72f5ae2700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000a2fa38 CR3: 00000001d7980000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff81b69a1f ffff8800b5957d58 00008000b5957d30 0000000041b58ab3
 ffffffff83fc82f2 ffffffff81b69980 0000000000000246 ffff8801d1096770
 ffff8801d3165668 ffffffff8157844b ffff8801d1095f00
 ffff880000000001
Call Trace:
[<ffffffff81b6a19d>] selinux_socket_setsockopt+0x4d/0x80 security/selinux/hooks.c:4338
[<ffffffff81b4873d>] security_socket_setsockopt+0x7d/0xb0 security/security.c:1257
[<ffffffff82df1ac8>] SYSC_setsockopt net/socket.c:1757 [inline]
[<ffffffff82df1ac8>] SyS_setsockopt+0xe8/0x250 net/socket.c:1746
[<ffffffff83776499>] entry_SYSCALL_64_fastpath+0x16/0x92
Code: c2 42 9b b6 81 be 01 00 00 00 48 c7 c7 a0 cb 2b 84 e8
f7 2f 6d ff 49 8d 7d 10 48 b8 00 00 00 00 00 fc ff df 48 89
fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 83 01 00
00 41 8b 75 10 31
RIP  [<ffffffff81b69b7e>] sock_has_perm+0x1fe/0x3e0 security/selinux/hooks.c:4069
RSP <ffff8800b5957ce0>
---[ end trace 7b5aaf788fef6174 ]---

In the absence of commit a4298e4522d6 ("net: add SOCK_RCU_FREE socket
flag") and all the associated infrastructure changes to take advantage
of a RCU grace period before freeing, there is a heightened
possibility that a security check is performed while an ill-timed
setsockopt call races in from user space.  It then is prudent to null
check sk_security, and if the case, reject the permissions.

This adjustment is orthogonal to infrastructure improvements that may
nullify the needed check, but should be added as good code hygiene.

Signed-off-by: Mark Salyzyn <salyzyn@xxxxxxxxxxx>
Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
Cc: Stephen Smalley <sds@xxxxxxxxxxxxx>
Cc: Eric Paris <eparis@xxxxxxxxxxxxxx>
Cc: James Morris <james.l.morris@xxxxxxxxxx>
Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx>
Cc: selinux@xxxxxxxxxxxxx
Cc: linux-security-module@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
---
This patch should be applied to all stable trees (author wants
minimum of 3.18, 4.4, 4.9 and 4.14)

 security/selinux/hooks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 8644d864e3c1..95d7c8143373 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4342,7 +4342,7 @@ static int sock_has_perm(struct sock *sk, u32 perms)
 	struct common_audit_data ad;
 	struct lsm_network_audit net = {0,};
 
-	if (sksec->sid == SECINITSID_KERNEL)
+	if (!sksec || sksec->sid == SECINITSID_KERNEL)
 		return 0;
 
 	ad.type = LSM_AUDIT_DATA_NET;
-- 
2.16.0.rc1.238.g530d649a79-goog