linux-kernel - Re: [PATCH] fix crash when using XFS on loopback

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: Windows password security audit tool. GUI, reports in PDF.

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

Date:	Mon, 6 Jan 2014 12:54:22 -0500 (EST)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	Andi Kleen <ak@...ux.intel.com>, Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@....fi>, linux-kernel@...r.kernel.org,
	linux-parisc@...r.kernel.org
Subject: Re: [PATCH] fix crash when using XFS on loopback

Hi

On Mon, 6 Jan 2014, Joonsoo Kim wrote:

> Hello,
> 
> I'm surprised that this VM_BUG_ON() has not been triggered until now. It was
> introduced in 2007 by commit (b5fab14). Maybe there is no person who test
> with CONFIG_DEBUG_VM.

Last time I tried it, PS-RISC didn't work with CONFIG_DEBUG_VM at all.

> There is one more bug report same as this.
> * possible regression on 3.13 when calling flush_dcache_page
>   (lkml.org/lkml/2013/12/12/255)

That link doesn't show anything.

> As mentioned in the description of commit (b5fab14), slab object may not be
> properly aligned and use of page oriented function to this object can be
> dangerous. I searched the XFS code and found that they only try to allocate
> multiple of 512 bytes, so there is no problem for now. But, IMHO, it is better
> not to use slab objects for this purpose.

If slab debugging is enabled, kmalloc memory is not aligned.

In XFS in xfs_buf_allocate_memory they test if the kmalloc memory crosses 
page boundary - if it does, they free the kmalloc memory and allocate a 
full page. Maybe this approach could still run into problems with some 
bus-master adapters that assume alignment in hardware...


dm-bufio also does I/O to slab-allocated buffers, but it allocates the 
object from slab (not kmalloc) with proper alignment.

> And I rapidly searched every callsites of page_mapping() and, IMHO, this 
> patch would work correctly. But possibly reverting original commit is 
> better solution.

Reverting the original commit wouldn't fix that VM_BUG_ON.

> Hello, Pekka and Christoph.
> Could you teach me which direction we have to go?
> 
> Thanks.

Mikulas
--
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/