SELinux: possible NULL deref in context_struct_to_string

It's possible that the caller passed a NULL for scontext.  However if this
is a defered mapping we might still attempt to call *scontext=kstrdup().
This is bad.  Instead just return the len.

Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 1ded0ec7e8c..9b7e7ed54e7 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -1018,9 +1018,11 @@ static int context_struct_to_string(struct context *context, char **scontext, u3
 
         if (context->len) {
                 *scontext_len = context->len;
-                *scontext = kstrdup(context->str, GFP_ATOMIC);
-                if (!(*scontext))
-                        return -ENOMEM;
+                if (scontext) {
+                        *scontext = kstrdup(context->str, GFP_ATOMIC);
+                        if (!(*scontext))
+                                return -ENOMEM;
+                }
                 return 0;
         }