linux-kernel - [16/68] CRED: Fix BUG() upon security_cred_alloc

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Message-Id: <20110228162407.244514776@clark.kroah.org>
Date:	Mon, 28 Feb 2011 08:22:37 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Howells <dhowells@...hat.com>
Subject: [16/68] CRED: Fix BUG() upon security_cred_alloc_blank() failure

2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

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@...ove.SAKURA.ne.jp>
Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 kernel/cred.c            |   12 ++++++++----
 security/selinux/hooks.c |    6 +++++-
 2 files changed, 13 insertions(+), 5 deletions(-)

--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -255,13 +255,13 @@ 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:
@@ -809,7 +809,11 @@ bool creds_are_invalid(const struct 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) ==
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3262,7 +3262,11 @@ static void selinux_cred_free(struct cre
 {
 	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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