linux-kernel - Re: [Linux-fbdev-devel] [2.6.29-rc2] fb_mmap: circular locking dependency on hibernation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 31 Jan 2009 19:11:55 +0100
From:	Andrea Righi <righi.andrea@...il.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	Andrey Borzenkov <arvidjaar@...l.ru>,
	Linux Frame Buffer Device Development 
	<linux-fbdev-devel@...ts.sourceforge.net>,
	"Antonino A. Daplas" <adaplas@...il.com>,
	linux-pm@...ts.linux-foundation.org,
	Linux Kernel Development <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-fbdev-devel] [2.6.29-rc2] fb_mmap: circular locking dependency
 on hibernation

On 2009-01-31 18:44, Geert Uytterhoeven wrote:
> On Sat, 31 Jan 2009, Andrea Righi wrote:
>> On 2009-01-30 05:15, Andrey Borzenkov wrote:
>>> On 29 of January 2009 12:10:11 Geert Uytterhoeven wrote:
>>>> On Tue, 27 Jan 2009, Andrey Borzenkov wrote:
>> fbcon: avoid circular locking dependency between fb_info->lock and mm->mmap_sem
>>
>> In fbcon notifier the handler for FB_EVENT_SET_CONSOLE_MAP doesn't need
>> to hold fb_info->lock.
>>
>> Simply unlock it before calling set_con2fb_map(), that could try to
>> acquire mm->mmap_sem to avoid a circular locking dependency with
>> fb_mmap() (that acquires mm->mmap_sem -> fb_info-lock).
> 
> However, set_con2fb_map() accesses the array of fb_info pointers
> registered_fb[], which seems to be a bit unsafe now the BKL is no longer held.

mmmh.. not sure about that, registered_fb[] was never accessed with
fb_info->lock held, see register/unregister_framebuffer().

But maybe this is another issue, and anyway, the array and also
num_registered_fb don't seem to be protected at all...

-Andrea
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/