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Commit 2edeaa34 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Linus Torvalds
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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: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 257a65d7

kernel/cred.c

+8 −4
Original line number Diff line number Diff line
@@ -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) ==

security/selinux/hooks.c

+5 −1
Original line number Diff line number Diff line
@@ -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);

}