linux-kernel - Re: [PATCH] kill suid bit only for regular files

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Date:	Mon, 27 Oct 2008 10:41:52 +0300
From:	Dmitri Monakhov <dmonakhov@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] kill suid bit only for regular files

Andrew Morton <akpm@...ux-foundation.org> writes:

> On Sun, 19 Oct 2008 18:00:39 +0400 Dmitri Monakhov <dmonakhov@...nvz.org> wrote:
>
>> We don't have to do it because it is useless for non regular files.
>
> Are we sure that should_remove_suid() is not and never will used for
> directories?
This bits are meaningless for directory. Posix is quiet about this case.
>
>> In fact block device may trigger this path without dentry->d_inode->i_mutex.
>
> What's wrong with blockdevs triggering this path?
We have following locking rules:notify_changes must be protected 
by d_inode->i_mutex.
BTW: You have add this sanity check to notify_change to -mm tree.
>
> Better changelogs, please.
Ok. Will do. My point is: it is improbable what some body(except me :) )
want to set S_ISUID/S_ISGID bit for non regular files. But it is 
technically possible and result in unexpected consequence.
>
>> Signed-off-by: Dmitri Monakhov <dmonakhov@...nvz.org>
>> ---
>>  mm/filemap.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>> 
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index a2907d5..3d5a2e7 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -1767,7 +1767,7 @@ int should_remove_suid(struct dentry *dentry)
>>  	if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
>>  		kill |= ATTR_KILL_SGID;
>>  
>> -	if (unlikely(kill && !capable(CAP_FSETID)))
>> +	if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
>>  		return kill;
>>  
>>  	return 0;
--
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