linux-kernel - Re: [PATCH usb] media/pvrusb2: fix uaf in pvr2_context_set

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Date: Sun, 18 Feb 2024 14:22:54 +0800
From: Edward Adam Davis <eadavis@...com>
To: greg@...ah.com
Cc: eadavis@...com,
	isely@...ox.com,
	linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org,
	linux-usb@...r.kernel.org,
	mchehab@...nel.org,
	pvrusb2-owner@...ly.net,
	pvrusb2@...ly.net,
	syzbot+ce750e124675d4599449@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH usb] media/pvrusb2: fix uaf in pvr2_context_set_notify

On Sat, 17 Feb 2024 08:41:33 +0100, Greg KH wrote:
> On Fri, Feb 16, 2024 at 03:30:47PM +0800, Edward Adam Davis wrote:
> > [Syzbot reported]
> > BUG: KASAN: slab-use-after-free in pvr2_context_set_notify+0x2c4/0x310 drivers/media/usb/pvrusb2/pvrusb2-context.c:35
> > Read of size 4 at addr ffff888113aeb0d8 by task kworker/1:1/26
> > 
> > CPU: 1 PID: 26 Comm: kworker/1:1 Not tainted 6.8.0-rc1-syzkaller-00046-gf1a27f081c1f #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
> > Workqueue: usb_hub_wq hub_event
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
> >  print_address_description mm/kasan/report.c:377 [inline]
> >  print_report+0xc4/0x620 mm/kasan/report.c:488
> >  kasan_report+0xda/0x110 mm/kasan/report.c:601
> >  pvr2_context_set_notify+0x2c4/0x310 drivers/media/usb/pvrusb2/pvrusb2-context.c:35
> >  pvr2_context_notify drivers/media/usb/pvrusb2/pvrusb2-context.c:95 [inline]
> >  pvr2_context_disconnect+0x94/0xb0 drivers/media/usb/pvrusb2/pvrusb2-context.c:272
> > 
> > Freed by task 906:
> > kasan_save_stack+0x33/0x50 mm/kasan/common.c:47
> > kasan_save_track+0x14/0x30 mm/kasan/common.c:68
> > kasan_save_free_info+0x3f/0x60 mm/kasan/generic.c:640
> > poison_slab_object mm/kasan/common.c:241 [inline]
> > __kasan_slab_free+0x106/0x1b0 mm/kasan/common.c:257
> > kasan_slab_free include/linux/kasan.h:184 [inline]
> > slab_free_hook mm/slub.c:2121 [inline]
> > slab_free mm/slub.c:4299 [inline]
> > kfree+0x105/0x340 mm/slub.c:4409
> > pvr2_context_check drivers/media/usb/pvrusb2/pvrusb2-context.c:137 [inline]
> > pvr2_context_thread_func+0x69d/0x960 drivers/media/usb/pvrusb2/pvrusb2-context.c:158
> > 
> > [Analyze]
> > Task A set disconnect_flag = !0, which resulted in Task B's condition being met
> > and releasing mp, leading to this issue.
> > 
> > [Fix]
> > Place the disconnect_flag assignment operation after all code in pvr2_context_disconnect()
> > to avoid this issue.
> > 
> > Reported-and-tested-by: syzbot+ce750e124675d4599449@...kaller.appspotmail.com
> > Signed-off-by: Edward Adam Davis <eadavis@...com>
> 
> What commit id does this fix?
e5be15c63804 ("V4L/DVB (7711): pvrusb2: Fix race on module unload")
> 
> And should it be cc: stable as well?
I checked the stable git tree and it introduced e5be15c63804. I think we need to
cc stable.

thanks,
edward