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 <[email protected]> Signed-off-by: David Howells <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
mna · Feb 7, 2011 · 2edeaa3 · 2edeaa3
1 parent 257a65d
commit 2edeaa3
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Showing 2 changed files with 13 additions and 5 deletions.
diff --git a/kernel/cred.c b/kernel/cred.c
@@ -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) ==

diff --git 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);
 }