CRED: Fix BUG() upon security_cred_alloc_blank() failure

commit 2edeaa34a6e3f2c43b667f6c4f7b27944b811695 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

diff --git a/kernel/cred.c b/kernel/cred.c
index 60bc8b1e32e632eb2a51b318f1ae35486d01174f..7d185fe6379f3311f497b4d9ddda13bad66a120a 100644 (file)
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -256,13 +256,13 @@ 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:
@@ -754,7 +754,11 @@ 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
index 49e55c041fa877d4e9276aef1d8e083375afaf2f..7b765f0c38dded355ba91939558abdf1769f8ea1 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3234,7 +3234,11 @@ 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);
 }