linux-ext4 - Re: repeatable inline-data oops (and fs corruption) caused by msync() of shared writable mmap (with recipe)

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Date:   Thu, 16 Mar 2017 16:13:01 +0000
From:   Nick Alcock <nix@...eri.org.uk>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org,
        Linux FS Mailing List <linux-fsdevel@...r.kernel.org>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: repeatable inline-data oops (and fs corruption) caused by msync() of shared writable mmap (with recipe)

On 16 Mar 2017, Jan Kara stated:

> On Tue 28-02-17 22:22:25, Nix wrote:
>> I first spotted this -- or it spotted me -- back in the v4.7.x days. It
>> is still present in v4.10.
>> 
>> Here's a replication recipe, given a reasonable rootfs with a compiler
>> on it, and assuming a blank virtio disk on /dev/vdb:
>
> Yup, the problem is that we mmap file with inline data without unpacking
> that and ext4_writepages() is unable to update inline data. Easy fix would
> be to unpack inline data in ext4_page_mkwrite(), somewhat more complicated
> fix would be to unpack inline data when extending file to too large size
> via truncate and handle writing into inode in ext4_writepages(). I'll have
> a look into fixing this. Thanks for report!

You probably want to talk to Eric Biggers, who posted a partial fix a
few days ago: <http://marc.info/?l=linux-ext4&m=148936608506059&w=2>