Asynchronous firmware loading copies the pointer to the
name passed as an argument only to be scheduled later and
used. This behaviour works well for synchronous calling
but in asynchronous mode there's a chance the caller could
immediately free the passed string after making the
asynchronous call. This could trigger a use after free
having the kernel look on disk for arbitrary file names.

In order to force-test the issue you can use a test-driver
designed to illustrate this issue on github [0], use the
next-20150505-fix-use-after-free branch.

With this patch applied you get:

[  283.512445] firmware name: test_module_stuff.bin
[  287.514020] firmware name: test_module_stuff.bin
[  287.532489] firmware found

Without this patch applied you can end up with something such as:

[  135.624216] firmware name: \xffffff80BJ
[  135.624249] platform fake-dev.0: Direct firmware load for \xffffff80Bi failed with error -2
[  135.624252] No firmware found
[  135.624252] firmware found

Unfortunatley in the worst and most common case however you
can typically crash your system with a page fault by trying to
free something which you cannot, and/or a NULL pointer
dereference [1].

The fix and issue using schedule_work() for asynchronous
runs is generalized in the following SmPL grammar patch,
when applied to next-20150505 only the firmware_class
code is affected. This grammar patch can and should further
be generalized to vet for for other kernel asynchronous
mechanisms.

@ calls_schedule_work @
type T;
T *priv_work;
identifier func, work_func;
identifier work;
identifier priv_name, name;
expression gfp;
@@

 func(..., const char *name, ...)
 {
 	...
 	priv_work = kzalloc(sizeof(T), gfp);
 	...
-	priv_work->priv_name = name;
+	priv_work->priv_name = kstrdup_const(name, gfp);
	...
(... when any
 	if (...)
 	{
 		...
+ 		kfree_const(priv_work->priv_name);
 		kfree(priv_work);
		...
 	}
) ... when any
 	INIT_WORK(&priv_work->work, work_func);
 	...
 	schedule_work(&priv_work->work);
 	...
 }

@ the_work_func depends on calls_schedule_work @
type calls_schedule_work.T;
T *priv_work;
identifier calls_schedule_work.work_func;
identifier calls_schedule_work.priv_name;
identifier calls_schedule_work.work;
identifier some_work;
@@

 work_func(...)
 {
 	...
 	priv_work = container_of(some_work, T, work);
 	...
+	kfree_const(priv_work->priv_name);
 	kfree(priv_work);
 	...
 }

[0] https://github.com/mcgrof/fake-firmware-test.git
[1] The following kernel ring buffer splat:

firmware name: test_module_stuff.bin
firmware name:
firmware found
general protection fault: 0000 [#1] SMP
Modules linked in: test(O) <...etc-it-does-not-matter>
 drm sr_mod cdrom xhci_pci xhci_hcd rtsx_pci mfd_core video button sg
CPU: 3 PID: 87 Comm: kworker/3:2 Tainted: G           O    4.0.0-00010-g22b5bb0-dirty #176
Hardware name: LENOVO 20AW000LUS/20AW000LUS, BIOS GLET43WW (1.18 ) 12/04/2013
Workqueue: events request_firmware_work_func
task: ffff8800c7f8e290 ti: ffff8800c7f94000 task.ti: ffff8800c7f94000
RIP: 0010:[<ffffffff814a586c>]  [<ffffffff814a586c>] fw_free_buf+0xc/0x40
RSP: 0000:ffff8800c7f97d78  EFLAGS: 00010286
RAX: ffffffff81ae3700 RBX: ffffffff816d1181 RCX: 0000000000000006
RDX: 0001ee850ff68500 RSI: 0000000000000246 RDI: c35d5f415e415d41
RBP: ffff8800c7f97d88 R08: 000000000000000a R09: 0000000000000000
R10: 0000000000000358 R11: ffff8800c7f97a7e R12: ffff8800c7ec1e80
R13: ffff88021e2d4cc0 R14: ffff88021e2dff00 R15: 00000000000000c0
FS:  0000000000000000(0000) GS:ffff88021e2c0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000034b8cd8 CR3: 000000021073c000 CR4: 00000000001407e0
Stack:
 ffffffff816d1181 ffff8800c7ec1e80 ffff8800c7f97da8 ffffffff814a58f8
 000000000000000a ffffffff816d1181 ffff8800c7f97dc8 ffffffffa047002c
 ffff88021e2dff00 ffff8802116ac1c0 ffff8800c7f97df8 ffffffff814a65fe
Call Trace:
 [<ffffffff816d1181>] ? __schedule+0x361/0x940
 [<ffffffff814a58f8>] release_firmware+0x58/0x80
 [<ffffffff816d1181>] ? __schedule+0x361/0x940
 [<ffffffffa047002c>] test_mod_cb+0x2c/0x43 [test]
 [<ffffffff814a65fe>] request_firmware_work_func+0x5e/0x80
 [<ffffffff816d1181>] ? __schedule+0x361/0x940
 [<ffffffff8108d23a>] process_one_work+0x14a/0x3f0
 [<ffffffff8108d911>] worker_thread+0x121/0x460
 [<ffffffff8108d7f0>] ? rescuer_thread+0x310/0x310
 [<ffffffff810928f9>] kthread+0xc9/0xe0
 [<ffffffff81092830>] ? kthread_create_on_node+0x180/0x180
 [<ffffffff816d52d8>] ret_from_fork+0x58/0x90
 [<ffffffff81092830>] ? kthread_create_on_node+0x180/0x180
Code: c7 c6 dd ad a3 81 48 c7 c7 20 97 ce 81 31 c0 e8 0b b2 ed ff e9 78 ff ff ff 66 0f 1f 44 00 00 0f 1f 44 00 00 55 48 89 e5 41 54 53 <4c> 8b 67 38 48 89 fb 4c 89 e7 e8 85 f7 22 00 f0 83 2b 01 74 0f
RIP  [<ffffffff814a586c>] fw_free_buf+0xc/0x40
 RSP <ffff8800c7f97d78>
---[ end trace 4e62c56a58d0eac1 ]---
BUG: unable to handle kernel paging request at ffffffffffffffd8
IP: [<ffffffff81093ee0>] kthread_data+0x10/0x20
PGD 1c13067 PUD 1c15067 PMD 0
Oops: 0000 [#2] SMP
Modules linked in: test(O) <...etc-it-does-not-matter>
 drm sr_mod cdrom xhci_pci xhci_hcd rtsx_pci mfd_core video button sg
CPU: 3 PID: 87 Comm: kworker/3:2 Tainted: G      D    O    4.0.0-00010-g22b5bb0-dirty #176
Hardware name: LENOVO 20AW000LUS/20AW000LUS, BIOS GLET43WW (1.18 ) 12/04/2013
task: ffff8800c7f8e290 ti: ffff8800c7f94000 task.ti: ffff8800c7f94000
RIP: 0010:[<ffffffff81092ee0>]  [<ffffffff81092ee0>] kthread_data+0x10/0x20
RSP: 0018:ffff8800c7f97b18  EFLAGS: 00010096
RAX: 0000000000000000 RBX: 0000000000000003 RCX: 000000000000000d
RDX: 0000000000000003 RSI: 0000000000000003 RDI: ffff8800c7f8e290
RBP: ffff8800c7f97b18 R08: 000000000000bc00 R09: 0000000000007e76
R10: 0000000000000001 R11: 000000000000002f R12: ffff8800c7f8e290
R13: 00000000000154c0 R14: 0000000000000003 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff88021e2c0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000028 CR3: 0000000210675000 CR4: 00000000001407e0
Stack:
 ffff8800c7f97b38 ffffffff8108dcd5 ffff8800c7f97b38 ffff88021e2d54c0
 ffff8800c7f97b88 ffffffff816d1500 ffff880213d42368 ffff8800c7f8e290
 ffff8800c7f97b88 ffff8800c7f97fd8 ffff8800c7f8e710 0000000000000246
Call Trace:
 [<ffffffff8108dcd5>] wq_worker_sleeping+0x15/0xa0
 [<ffffffff816d1500>] __schedule+0x6e0/0x940
 [<ffffffff816d1797>] schedule+0x37/0x90
 [<ffffffff810779bc>] do_exit+0x6bc/0xb40
 [<ffffffff8101898f>] oops_end+0x9f/0xe0
 [<ffffffff81018efb>] die+0x4b/0x70
 [<ffffffff81015622>] do_general_protection+0xe2/0x170
 [<ffffffff816d74e8>] general_protection+0x28/0x30
 [<ffffffff816d1181>] ? __schedule+0x361/0x940
 [<ffffffff814a586c>] ? fw_free_buf+0xc/0x40
 [<ffffffff816d1181>] ? __schedule+0x361/0x940
 [<ffffffff814a58f8>] release_firmware+0x58/0x80
 [<ffffffff816d1181>] ? __schedule+0x361/0x940
 [<ffffffffa047002c>] test_mod_cb+0x2c/0x43 [test]
 [<ffffffff814a65fe>] request_firmware_work_func+0x5e/0x80
 [<ffffffff816d1181>] ? __schedule+0x361/0x940
 [<ffffffff8108d23a>] process_one_work+0x14a/0x3f0
 [<ffffffff8108d911>] worker_thread+0x121/0x460
 [<ffffffff8108d7f0>] ? rescuer_thread+0x310/0x310
 [<ffffffff810928f9>] kthread+0xc9/0xe0
 [<ffffffff81092830>] ? kthread_create_on_node+0x180/0x180
 [<ffffffff816d52d8>] ret_from_fork+0x58/0x90
 [<ffffffff81092830>] ? kthread_create_on_node+0x180/0x180
Code: 00 48 89 e5 5d 48 8b 40 c8 48 c1 e8 02 83 e0 01 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 8b 87 30 05 00 00 55 48 89 e5 <48> 8b 40 d8 5d c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00
RIP  [<ffffffff81092ee0>] kthread_data+0x10/0x20
 RSP <ffff8800c7f97b18>
CR2: ffffffffffffffd8
---[ end trace 4e62c56a58d0eac2 ]---
Fixing recursive fault but reboot is needed!

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: David Howells <dhowells@redhat.com>
Cc: Ming Lei <ming.lei@canonical.com>
Cc: Seth Forshee <seth.forshee@canonical.com>
Cc: Kyle McMartin <kyle@kernel.org>
Generated-by: Coccinelle SmPL
Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>