CRED: Fix BUG() upon security_cred_alloc_blank() failure
Tetsuo Handa [Mon, 7 Feb 2011 13:36:10 +0000 (13:36 +0000)]
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>

kernel/cred.c
security/selinux/hooks.c

index 6a1aa00..fcf104b 100644 (file)
@@ -252,13 +252,13 @@ struct cred *cred_alloc_blank(void)
 #endif
 
        atomic_set(&new->usage, 1);
+#ifdef CONFIG_DEBUG_CREDENTIALS
+       new->magic = CRED_MAGIC;
+#endif
 
        if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
                goto error;
 
-#ifdef CONFIG_DEBUG_CREDENTIALS
-       new->magic = CRED_MAGIC;
-#endif
        return new;
 
 error:
@@ -748,7 +748,11 @@ bool creds_are_invalid(const struct cred *cred)
        if (cred->magic != CRED_MAGIC)
                return true;
 #ifdef CONFIG_SECURITY_SELINUX
-       if (selinux_is_enabled()) {
+       /*
+        * cred->security == NULL if security_cred_alloc_blank() or
+        * security_prepare_creds() returned an error.
+        */
+       if (selinux_is_enabled() && cred->security) {
                if ((unsigned long) cred->security < PAGE_SIZE)
                        return true;
                if ((*(u32 *)cred->security & 0xffffff00) ==
index e276eb4..c8d6992 100644 (file)
@@ -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);
 }