[PATCH] net: fix memory leak in security_sk_alloc()

[Wang Yufen]

kmemleak reports this issue:

unreferenced object 0xffff88810b7835c0 (size 32):
  comm "test_progs", pid 270, jiffies 4294969007 (age 1621.315s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    03 00 00 00 03 00 00 00 0f 00 00 00 00 00 00 00  ................
  backtrace:
    [<00000000376cdeab>] kmalloc_trace+0x27/0x110
    [<000000003bcdb3b6>] selinux_sk_alloc_security+0x66/0x110
    [<000000003959008f>] security_sk_alloc+0x47/0x80
    [<00000000e7bc6668>] sk_prot_alloc+0xbd/0x1a0
    [<0000000002d6343a>] sk_alloc+0x3b/0x940
    [<000000009812a46d>] unix_create1+0x8f/0x3d0
    [<000000005ed0976b>] unix_create+0xa1/0x150
    [<0000000086a1d27f>] __sock_create+0x233/0x4a0
    [<00000000cffe3a73>] __sys_socket_create.part.0+0xaa/0x110
    [<0000000007c63f20>] __sys_socket+0x49/0xf0
    [<00000000b08753c8>] __x64_sys_socket+0x42/0x50
    [<00000000b56e26b3>] do_syscall_64+0x3b/0x90
    [<000000009b4871b8>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

The issue occurs in the following scenarios:

unix_create1()
  sk_alloc()
    sk_prot_alloc()
      security_sk_alloc()
        call_int_hook()
          hlist_for_each_entry()
            entry1->hook.sk_alloc_security
            <-- selinux_sk_alloc_security() succeeded,
            <-- sk->security alloced here.
            entry2->hook.sk_alloc_security
            <-- bpf_lsm_sk_alloc_security() failed
      goto out_free;
        ...    <-- the sk->security not freed, memleak

To fix, if security_sk_alloc() failed and sk->security not null,
goto out_free_sec to reclaim resources.

I'm not sure whether this fix makes sense, but if hook lists don't
support this usage, might need to modify the
"tools/testing/selftests/bpf/progs/lsm_cgroup.c" test case.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Wang Yufen <wangyufen at huawei.com>
Cc: Stanislav Fomichev <sdf at google.com>
---
 net/core/sock.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index a3ba035..e457a9d 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2030,8 +2030,11 @@ static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,
 		sk = kmalloc(prot->obj_size, priority);
 
 	if (sk != NULL) {
-		if (security_sk_alloc(sk, family, priority))
+		if (security_sk_alloc(sk, family, priority)) {
+			if (sk->sk_security)
+				goto out_free_sec;
 			goto out_free;
+		}
 
 		if (!try_module_get(prot->owner))
 			goto out_free_sec;
-- 
1.8.3.1