[lkml]   [2011]   [Feb]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] Check for immutable flag in fallocate path
2011/2/27 Ted Ts'o <>:
> On Mon, Feb 21, 2011 at 05:50:21PM +0100, Marco Stornelli wrote:
>> 2011/2/21 Christoph Hellwig <>:
>> > On Mon, Feb 21, 2011 at 09:26:32AM +0100, Marco Stornelli wrote:
>> >> From: Marco Stornelli <>
>> >>
>> >> All fs must check for the immutable flag in their fallocate callback.
>> >> 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. Only Ocfs2 check for the immutable flag at the
>> >> moment.
>> >
>> > Please add the check in fs/open.c:do_fallocate() so that it covers all
>> > filesystems.
>> >
>> >
>> The check should be done after the fs got the inode mutex lock.
> Why?  None of the other places which check the IMMUTABLE flag do so
> under the inode mutex lock.  Yes, it's true that we're not properly
> doing proper locking when updating i_flags from the ioctl (this is
> true for all file systems), but this has been true for quite some
> time, and using a mutex to protect bit set/clear/test operations would
> be like using a sledgehammer to kill a fly.
> A proper fix if we want to be completely correct about updates to
> i_flags would involve using test_bit, set_bit, and clear_bit, which is
> guaranteed to be atomic.  This is how we update the
> ext4_inode_info->i_flags (which is different from inode->i_flags) (see
> the definition and use of EXT4_INODE_BIT_FNS in fs/ext4/ext4.h).
> At some point, it would be good to fix how we set/get i_flags values,
> but that's independent of the change that's being discussed here.
>                                                  - Ted

I was thinking to the possible race with setattr callback.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2011-02-28 08:55    [W:0.079 / U:5.712 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site