Re: [PATCH 1/3] ext3: Fix data / filesystem corruption when write fails to copy data

[Jan Kara <jack@suse.cz>]

  Hi,

On Wed 09-12-09 17:42:12, saeed bishara wrote:
> I came a cross data corruption bug when using ext3, this patch fixed
> it. the bug exists in 2.6.31 and 32.
  Yes, I plan to send the fix to stable@kernel.org so that it gets fixed in
the stable releases for these kernels as well. Thanks for your notice.

									Honza

> On Wed, Dec 2, 2009 at 9:16 PM, Jan Kara <jack@suse.cz> wrote:
> > When ext3_write_begin fails after allocating some blocks or
> > generic_perform_write fails to copy data to write, we truncate blocks already
> > instantiated beyond i_size. Although these blocks were never inside i_size, we
> > have to truncate pagecache of these blocks so that corresponding buffers get
> > unmapped. Otherwise subsequent __block_prepare_write (called because we are
> > retrying the write) will find the buffers mapped, not call ->get_block, and
> > thus the page will be backed by already freed blocks leading to filesystem and
> > data corruption.
> >
> > CC: linux-ext4@vger.kernel.org
> > Reported-by: James Y Knight <foom@fuhm.net>
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> >  fs/ext3/inode.c |   18 ++++++++++++++----
> >  1 files changed, 14 insertions(+), 4 deletions(-)
> >
> > I will take care of merging this patch. I'm just sending it for completeness...
> >
> > diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c
> > index 354ed3b..f9d6937 100644
> > --- a/fs/ext3/inode.c
> > +++ b/fs/ext3/inode.c
> > @@ -1151,6 +1151,16 @@ static int do_journal_get_write_access(handle_t *handle,
> >        return ext3_journal_get_write_access(handle, bh);
> >  }
> >
> > +/*
> > + * Truncate blocks that were not used by write. We have to truncate the
> > + * pagecache as well so that corresponding buffers get properly unmapped.
> > + */
> > +static void ext3_truncate_failed_write(struct inode *inode)
> > +{
> > +       truncate_inode_pages(inode->i_mapping, inode->i_size);
> > +       ext3_truncate(inode);
> > +}
> > +
> >  static int ext3_write_begin(struct file *file, struct address_space *mapping,
> >                                loff_t pos, unsigned len, unsigned flags,
> >                                struct page **pagep, void **fsdata)
> > @@ -1209,7 +1219,7 @@ write_begin_failed:
> >                unlock_page(page);
> >                page_cache_release(page);
> >                if (pos + len > inode->i_size)
> > -                       ext3_truncate(inode);
> > +                       ext3_truncate_failed_write(inode);
> >        }
> >        if (ret == -ENOSPC && ext3_should_retry_alloc(inode->i_sb, &retries))
> >                goto retry;
> > @@ -1304,7 +1314,7 @@ static int ext3_ordered_write_end(struct file *file,
> >        page_cache_release(page);
> >
> >        if (pos + len > inode->i_size)
> > -               ext3_truncate(inode);
> > +               ext3_truncate_failed_write(inode);
> >        return ret ? ret : copied;
> >  }
> >
> > @@ -1330,7 +1340,7 @@ static int ext3_writeback_write_end(struct file *file,
> >        page_cache_release(page);
> >
> >        if (pos + len > inode->i_size)
> > -               ext3_truncate(inode);
> > +               ext3_truncate_failed_write(inode);
> >        return ret ? ret : copied;
> >  }
> >
> > @@ -1383,7 +1393,7 @@ static int ext3_journalled_write_end(struct file *file,
> >        page_cache_release(page);
> >
> >        if (pos + len > inode->i_size)
> > -               ext3_truncate(inode);
> > +               ext3_truncate_failed_write(inode);
> >        return ret ? ret : copied;
> >  }
> >
> > --
> > 1.6.4.2
> >
> > --
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> >
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR