[PATCH v3] selinux: lsm: fix a missing-check bug in selinux_add_mnt_opt( )

[Gen Zhang]

In selinux_add_mnt_opt(), 'val' is allocated by kmemdup_nul(). It returns
NULL when fails. So 'val' should be checked. And 'mnt_opts' should be 
freed when error.

Signed-off-by: Gen Zhang <blackgod016...@gmail.com>
Fixes: 757cbe597fe8 ("LSM: new method: ->sb_add_mnt_opt()")
---
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 3ec702c..4e4c1c6 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1052,15 +1052,23 @@ static int selinux_add_mnt_opt(const char *option, 
const char *val, int len,
        if (token == Opt_error)
                return -EINVAL;
 
-       if (token != Opt_seclabel)
-               val = kmemdup_nul(val, len, GFP_KERNEL);
+       if (token != Opt_seclabel) {
+                       val = kmemdup_nul(val, len, GFP_KERNEL);
+                       if (!val) {
+                               rc = -ENOMEM;
+                               goto free_opt;
+                       }
+       }
        rc = selinux_add_opt(token, val, mnt_opts);
        if (unlikely(rc)) {
                kfree(val);
-               if (*mnt_opts) {
-                       selinux_free_mnt_opts(*mnt_opts);
-                       *mnt_opts = NULL;
-               }
+               goto free_opt;
+       }
+       return rc;
+free_opt:
+       if (*mnt_opts) {
+               selinux_free_mnt_opts(*mnt_opts);
+               *mnt_opts = NULL;
        }
        return rc;
 }