Re: [RFT] [media] em28xx: Fix use-after-free in v4l2_fh_init

[Andrey Konovalov]

On Thu, Nov 9, 2017 at 6:49 AM, Arvind Yadav  wrote:
> Here, em28xx_free_v4l2 is release "v4l2->dev->v4l2"
> Which is allready release by em28xx_v4l2_init.
>
> Signed-off-by: Arvind Yadav 

Hi Arvind,

I still see the crash with your patch.

Thanks!

em28xx 1-1:0.0: Disconnecting
em28xx 1-1:0.0: Registering V4L2 extension
em28xx 1-1:0.0: Config register raw data: 0xffed
em28xx 1-1:0.0: AC97 chip type couldn't be determined
em28xx 1-1:0.0: No AC97 audio processor
em28xx 1-1:0.0: failed to create media graph
em28xx 1-1:0.0: V4L2 device video0 deregistered
em28xx 1-1:0.0: Binding DVB extension
==
BUG: KASAN: use-after-free in v4l2_fh_init+0x239/0x280
Read of size 8 at addr 88006b40c998 by task v4l_id/5917

CPU: 0 PID: 5917 Comm: v4l_id Not tainted
4.14.0-rc8-44455-ge2105594a876-dirty #102
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17
 dump_stack+0xe1/0x157 lib/dump_stack.c:53
 print_address_description+0x71/0x234 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351
 kasan_report+0x173/0x270 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x19/0x20 mm/kasan/report.c:430
 v4l2_fh_init+0x239/0x280 drivers/media/v4l2-core/v4l2-fh.c:33
 v4l2_fh_open+0x76/0xa0 drivers/media/v4l2-core/v4l2-fh.c:70
 em28xx_v4l2_open+0x252/0x6f0 drivers/media/usb/em28xx/em28xx-video.c:2060
 v4l2_open+0x1b7/0x380 drivers/media/v4l2-core/v4l2-dev.c:425
 chrdev_open+0x1db/0x520 fs/char_dev.c:417
 do_dentry_open+0x735/0xe20 fs/open.c:752
 vfs_open+0x13e/0x230 fs/open.c:866
 do_last fs/namei.c:3388
 path_openat+0x722/0x2860 fs/namei.c:3528
 do_filp_open+0x13f/0x1d0 fs/namei.c:3563
 do_sys_open+0x362/0x4c0 fs/open.c:1059
 SYSC_open fs/open.c:1077
 SyS_open+0x32/0x40 fs/open.c:1072
 entry_SYSCALL_64_fastpath+0x23/0xc2 arch/x86/entry/entry_64.S:203
RIP: 0033:0x7faff04be120
RSP: 002b:7fff4d967aa8 EFLAGS: 0246 ORIG_RAX: 0002
RAX: ffda RBX: 0046 RCX: 7faff04be120
RDX: 7faff0773138 RSI:  RDI: 7fff4d967f1e
RBP:  R08:  R09: 
R10:  R11: 0246 R12: 00400884
R13: 7fff4d967c00 R14:  R15: 

Allocated by task 3170:
 save_stack_trace+0x1b/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459
 kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x11a/0x290 mm/slub.c:2773
 kmalloc ./include/linux/slab.h:494
 kzalloc ./include/linux/slab.h:667
 em28xx_v4l2_init+0x10c/0x3660 drivers/media/usb/em28xx/em28xx-video.c:2438
 em28xx_init_extension+0x11a/0x190 drivers/media/usb/em28xx/em28xx-core.c:1110
 request_module_async+0x6a/0x80 drivers/media/usb/em28xx/em28xx-cards.c:3161
 process_one_work+0x925/0x15d0 kernel/workqueue.c:2113
 process_scheduled_works kernel/workqueue.c:2173
 worker_thread+0x6c0/0x10d0 kernel/workqueue.c:2252
 kthread+0x346/0x410 kernel/kthread.c:231
 ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:432

Freed by task 3170:
 save_stack_trace+0x1b/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459
 kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:524
 slab_free_hook mm/slub.c:1391
 slab_free_freelist_hook mm/slub.c:1413
 slab_free mm/slub.c:2989
 kfree+0xf2/0x2e0 mm/slub.c:3920
 em28xx_free_v4l2 drivers/media/usb/em28xx/em28xx-video.c:2025
 kref_put ./include/linux/kref.h:70
 em28xx_v4l2_init+0x2382/0x3660 drivers/media/usb/em28xx/em28xx-video.c:2788
 em28xx_init_extension+0x11a/0x190 drivers/media/usb/em28xx/em28xx-core.c:1110
 request_module_async+0x6a/0x80 drivers/media/usb/em28xx/em28xx-cards.c:3161
 process_one_work+0x925/0x15d0 kernel/workqueue.c:2113
 process_scheduled_works kernel/workqueue.c:2173
 worker_thread+0x6c0/0x10d0 kernel/workqueue.c:2252
 kthread+0x346/0x410 kernel/kthread.c:231
 ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:432

The buggy address belongs to the object at 88006b40c200
 which belongs to the cache kmalloc-8192 of size 8192
The buggy address is located 1944 bytes inside of
 8192-byte region [88006b40c200, 88006b40e200)
The buggy address belongs to the page:
page:ea0001ad0200 count:1 mapcount:0 mapping:  (null)
index:0x0 compound_mapcount: 0
flags: 0x1008100(slab|head)
raw: 01008100   000180030003
raw:  00010001 88006c402a80 
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 88006b40c880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 88006b40c900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>88006b40c980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
 88006b40ca00: fb 

[RFT] [media] em28xx: Fix use-after-free in v4l2_fh_init

[Arvind Yadav]

Here, em28xx_free_v4l2 is release "v4l2->dev->v4l2"
Which is allready release by em28xx_v4l2_init.

Signed-off-by: Arvind Yadav 
---
This bug report by Andrey Konovalov "net/media/em28xx: use-after-free in 
v4l2_fh_init"

 drivers/media/usb/em28xx/em28xx-video.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/usb/em28xx/em28xx-video.c 
b/drivers/media/usb/em28xx/em28xx-video.c
index 8d253a5..f1ee53f 100644
--- a/drivers/media/usb/em28xx/em28xx-video.c
+++ b/drivers/media/usb/em28xx/em28xx-video.c
@@ -2785,8 +2785,8 @@ static int em28xx_v4l2_init(struct em28xx *dev)
v4l2_ctrl_handler_free(>ctrl_handler);
v4l2_device_unregister(>v4l2_dev);
 err:
-   dev->v4l2 = NULL;
kref_put(>ref, em28xx_free_v4l2);
+   dev->v4l2 = NULL;
mutex_unlock(>lock);
return ret;
 }
-- 
1.9.1