Commit 2480f57f authored Dec 02, 2013 by David Howells

KEYS: Pre-clear struct key on allocation



The second word of key->payload does not get initialised in key_alloc(), but
the big_key type is relying on it having been cleared.  The problem comes when
big_key fails to instantiate a large key and doesn't then set the payload.  The
big_key_destroy() op is called from the garbage collector and this assumes that
the dentry pointer stored in the second word will be NULL if instantiation did
not complete.

Therefore just pre-clear the entire struct key on allocation rather than trying
to be clever and only initialising to 0 only those bits that aren't otherwise
initialised.

The lack of initialisation can lead to a bug report like the following if
big_key failed to initialise its file:

	general protection fault: 0000 [#1] SMP
	Modules linked in: ...
	CPU: 0 PID: 51 Comm: kworker/0:1 Not tainted 3.10.0-53.el7.x86_64 #1
	Hardware name: Dell Inc. PowerEdge 1955/0HC513, BIOS 1.4.4 12/09/2008
	Workqueue: events key_garbage_collector
	task: ffff8801294f5680 ti: ffff8801296e2000 task.ti: ffff8801296e2000
	RIP: 0010:[<ffffffff811b4a51>] dput+0x21/0x2d0
	...
	Call Trace:
	 [<ffffffff811a7b06>] path_put+0x16/0x30
	 [<ffffffff81235604>] big_key_destroy+0x44/0x60
	 [<ffffffff8122dc4b>] key_gc_unused_keys.constprop.2+0x5b/0xe0
	 [<ffffffff8122df2f>] key_garbage_collector+0x1df/0x3c0
	 [<ffffffff8107759b>] process_one_work+0x17b/0x460
	 [<ffffffff8107834b>] worker_thread+0x11b/0x400
	 [<ffffffff81078230>] ? rescuer_thread+0x3e0/0x3e0
	 [<ffffffff8107eb00>] kthread+0xc0/0xd0
	 [<ffffffff8107ea40>] ? kthread_create_on_node+0x110/0x110
	 [<ffffffff815c4bec>] ret_from_fork+0x7c/0xb0
	 [<ffffffff8107ea40>] ? kthread_create_on_node+0x110/0x110

Reported-by: Patrik Kis <pkis@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Stephen Gallagher <sgallagh@redhat.com>

parent af91706d

security/keys/key.c

+1 −7

Original line number	Diff line number	Diff line
		@@ -272,7 +272,7 @@ struct key key_alloc(struct key_type type, const char *desc,
		}

		/* allocate and initialise the key and its description */
		key = kmem_cache_alloc(key_jar, GFP_KERNEL);
		key = kmem_cache_zalloc(key_jar, GFP_KERNEL);
		if (!key)
		goto no_memory_2;

		@@ -293,18 +293,12 @@ struct key key_alloc(struct key_type type, const char *desc,
		key->uid = uid;
		key->gid = gid;
		key->perm = perm;
		key->flags = 0;
		key->expiry = 0;
		key->payload.data = NULL;
		key->security = NULL;

		if (!(flags & KEY_ALLOC_NOT_IN_QUOTA))
		key->flags \|= 1 << KEY_FLAG_IN_QUOTA;
		if (flags & KEY_ALLOC_TRUSTED)
		key->flags \|= 1 << KEY_FLAG_TRUSTED;

		memset(&key->type_data, 0, sizeof(key->type_data));

		#ifdef KEY_DEBUGGING
		key->magic = KEY_DEBUG_MAGIC;
		#endif

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