CRED: Fix BUG() upon security_cred_alloc_blank() failure

In cred_alloc_blank() since 2.6.32, abort_creds(new) is called with
new->security == NULL and new->magic == 0 when security_cred_alloc_blank()
returns an error.  As a result, BUG() will be triggered if SELinux is enabled
or CONFIG_DEBUG_CREDENTIALS=y.

If CONFIG_DEBUG_CREDENTIALS=y, BUG() is called from __invalid_creds() because
cred->magic == 0.  Failing that, BUG() is called from selinux_cred_free()
because selinux_cred_free() is not expecting cred->security == NULL.  This does
not affect smack_cred_free(), tomoyo_cred_free() or apparmor_cred_free().

Fix these bugs by

(1) Set new->magic before calling security_cred_alloc_blank().

(2) Handle null cred->security in creds_are_invalid() and selinux_cred_free().

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e276eb468536..c8d699270687 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3198,7 +3198,11 @@ static void selinux_cred_free(struct cred *cred)
 {
         struct task_security_struct *tsec = cred->security;
 
-        BUG_ON((unsigned long) cred->security < PAGE_SIZE);
+        /*
+         * cred->security == NULL if security_cred_alloc_blank() or
+         * security_prepare_creds() returned an error.
+         */
+        BUG_ON(cred->security && (unsigned long) cred->security < PAGE_SIZE);
         cred->security = (void *) 0x7UL;
         kfree(tsec);
 }