linux-ext4 - Re: [PATCH v3] Fix ext4 fault handling when mounted with -o dax,ro

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]

Message-ID: <20170824151138.GA25588@linux.intel.com>
Date:   Thu, 24 Aug 2017 09:11:38 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     rdodgen@...il.com
Cc:     tytso@....edu, linux-ext4@...r.kernel.org,
        ross.zwisler@...ux.intel.com, Randy Dodgen <dodgen@...gle.com>,
        linux-nvdimm@...ts.01.org
Subject: Re: [PATCH v3] Fix ext4 fault handling when mounted with -o dax,ro

On Wed, Aug 23, 2017 at 02:26:52PM -0700, rdodgen@...il.com wrote:
> From: Randy Dodgen <dodgen@...gle.com>
> 
> If an ext4 filesystem is mounted with both the DAX and read-only
> options, executables on that filesystem will fail to start (claiming
> 'Segmentation fault') due to the fault handler returning
> VM_FAULT_SIGBUS.
> 
> This is due to the DAX fault handler (see ext4_dax_huge_fault)
> attempting to write to the journal when FAULT_FLAG_WRITE is set. This is
> the wrong behavior for write faults which will lead to a COW page; in
> particular, this fails for readonly mounts.
> 
> This change avoids journal writes for faults that are expected to COW.
> 
> It might be the case that this could be better handled in
> ext4_iomap_begin / ext4_iomap_end (called via iomap_ops inside
> dax_iomap_fault). These is some overlap already (e.g. grabbing journal
> handles).
> 
> Signed-off-by: Randy Dodgen <dodgen@...gle.com>

Cool, looks good from the DAX point of view.  You can add:

Reviewed-by: Ross Zwisler <ross.zwisler@...ux.intel.com>