lkml.org 
[lkml]   [2011]   [Mar]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v3] Check for immutable/append flag in fallocate path
From
Date
On 2011-03-07, at 10:11 PM, Dave Chinner wrote:
> On Sat, Mar 05, 2011 at 10:37:45AM +0100, Marco Stornelli wrote:
>> From: Marco Stornelli <marco.stornelli@gmail.com>
>>
>> In the fallocate path the kernel doesn't check for the immutable/append
>> flag. It's possible to have a race condition in this scenario: an
>> application open a file in read/write and it does something, meanwhile
>> root set the immutable flag on the file, the application at that point
>> can call fallocate with success. In addition, we don't allow to do any
>> unreserve operation on an append only file but only the reserve one.
>>
>> Signed-off-by: Marco Stornelli <marco.stornelli@gmail.com>
>> ---
>> Patch is against 2.6.38-rc7
>>
>> ChangeLog:
>> v3: Modified do_fallocate instead of every single fs
>> v2: Added the check for append-only file for XFS
>> v1: First draft
>>
>> --- open.c.orig 2011-03-01 22:55:12.000000000 +0100
>> +++ open.c 2011-03-04 15:28:43.000000000 +0100
>> @@ -233,6 +233,14 @@ int do_fallocate(struct file *file, int
>>
>> if (!(file->f_mode & FMODE_WRITE))
>> return -EBADF;
>> +
>> + /* It's not possible punch hole on append only file */
>> + if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode))
>> + return -EPERM;
>
> Seeing as I didn't get an answer in before you reposted, I still
> think punching an append-only file is a valid thing to want to do.
>
> I've seen this done in the past for application-level transaction
> journal files. The journal file is append only so new transactions
> can only be written at the end of the file i.e. you cannot overwrite
> (and therefore corrupt) existing transactions. However, once a
> transaction is complete and the changes flushed to disk, the
> transaction is punched out of the file to zero the range so it
> doesn't get replayed during recovery after a system crash.

To my thinking "append only" means just that - only new data can be written at the end of the file, and existing data cannot be modified. Allowing hole punch on such a file (e.g. range 0 .. ~0) would allow erasing all of the data, entirely bypassing the append-only flag.

Cheers, Andreas







\
 
 \ /
  Last update: 2011-03-08 06:41    [from the cache]
©2003-2011 Jasper Spaans