Commit 012146d0 authored Aug 22, 2011 by David Howells Committed by James Morris Aug 23, 2011

CRED: Fix prepare_kernel_cred() to provide a new thread_group_cred struct



Fix prepare_kernel_cred() to provide a new, separate thread_group_cred struct
otherwise when using request_key() ____call_usermodehelper() calls
umh_keys_init() with the new creds pointing to init_tgcred, which
umh_keys_init() then blithely alters.

The problem can be demonstrated by:

	# keyctl request2 user a debug:a @s
	249681132
	# grep req /proc/keys
	079906a5 I--Q--     1 perm 1f3f0000     0     0 keyring   _req.249681132: 1/4
	38ef1626 IR----     1 expd 0b010000     0     0 .request_ key:ee1d4ec pid:4371 ci:1

The keyring _req.XXXX should have gone away, but something (init_tgcred) is
pinning it.

That key actually requested can then be removed and a new one created:

	# keyctl unlink 249681132
	1 links removed
	[root@andromeda ~]# grep req /proc/keys
	116cecac IR----     1 expd 0b010000     0     0 .request_ key:eeb4911 pid:4379 ci:1
	36d1cbf8 I--Q--     1 perm 1f3f0000     0     0 keyring   _req.250300689: 1/4

which causes the old _req keyring to go away and a new one to take its place.

This is a consequence of the changes in:

	commit 87966996
	Author: David Howells <dhowells@redhat.com>
	Date:   Fri Jun 17 11:25:59 2011 +0100
	KEYS/DNS: Fix ____call_usermodehelper() to not lose the session keyring

and:

	commit 17f60a7d
	Author: Eric Paris <eparis@redhat.com>
	Date:   Fri Apr 1 17:07:50 2011 -0400
	capabilites: allow the application of capability limits to usermode helpers

After this patch is applied, the _req keyring and the .request_key key are
cleaned up.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

parent 6d528b08

kernel/cred.c

+14 −2

Original line number	Diff line number	Diff line
		@@ -646,6 +646,9 @@ void __init cred_init(void)
		*/
		struct cred prepare_kernel_cred(struct task_struct daemon)
		{
		#ifdef CONFIG_KEYS
		struct thread_group_cred *tgcred;
		#endif
		const struct cred *old;
		struct cred *new;

		@@ -653,6 +656,12 @@ struct cred prepare_kernel_cred(struct task_struct daemon)
		if (!new)
		return NULL;

		tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
		if (!tgcred) {
		kmem_cache_free(cred_jar, new);
		return NULL;
		}

		kdebug("prepare_kernel_cred() alloc %p", new);

		if (daemon)
		@@ -669,8 +678,11 @@ struct cred prepare_kernel_cred(struct task_struct daemon)
		get_group_info(new->group_info);

		#ifdef CONFIG_KEYS
		atomic_inc(&init_tgcred.usage);
		new->tgcred = &init_tgcred;
		atomic_set(&tgcred->usage, 1);
		spin_lock_init(&tgcred->lock);
		tgcred->process_keyring = NULL;
		tgcred->session_keyring = NULL;
		new->tgcred = tgcred;
		new->request_key_auth = NULL;
		new->thread_keyring = NULL;
		new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;

Admin message