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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>
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1 parent 87a3ba7 commit d33edecb4561f33f276937feb6f74ab3e192bd8a Tetsuo Handa committed with Kali-
Showing with 13 additions and 5 deletions.
  1. +8 −4 kernel/cred.c
  2. +5 −1 security/selinux/hooks.c
View
12 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) ==
View
6 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);
}

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