linux-kernel - Re: [PATCH] kernfs: fix off by one error.

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Message-ID: <87k3c8ze81.fsf@xmission.com>
Date:	Wed, 05 Mar 2014 10:34:38 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Richard Cochran <richardcochran@...il.com>,
	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	stable@...r.kernel.org
Subject: Re: [PATCH] kernfs: fix off by one error.

Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:

> On Wed, Mar 05, 2014 at 05:10:52PM +0100, Richard Cochran wrote:
>> The hash values 0 and 1 are reserved for magic directory entries, but
>> the code only prevents names hashing to 0. This patch fixes the test
>> to also prevent hash value 1.
>> 
>> Signed-off-by: Richard Cochran <richardcochran@...il.com>
>> Cc: <stable@...r.kernel.org>
>> ---
>>  fs/kernfs/dir.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Is this for 3.14-final or 3.15-rc1?

The bug has existed since I added that hash function in 3.4-rc1.  It was
named sysfs_name_hash then but the code has otherwise been unchanged.

It is a very minor bug.

commit 4e4d6d860b9393c5395ba5920edb5b4c5d43a3a3
Author: Eric W. Biederman <ebiederm@...ssion.com>
Date:   Sun Dec 18 20:05:43 2011 -0800

    sysfs: Add s_hash to sysfs_dirent and order directory entries by hash
    
    Compute a 31 bit hash of directory entries (that can fit in a signed
    32bit off_t) and index the sysfs directory entries by that hash,
    replacing the per directory indexes by name and by inode.  Because we
    now only use a single rbtree this reduces the size of sysfs_dirent by 2
    pointers.  Because we have fewer cases to deal with the code is now
    simpler.
    
    For now I use the simple hash that the dcache uses as that is easy to
    use and seems simple enough.
    
    In addition to makeing the code simpler using a hash for the file
    position in readdir brings sysfs in line with other filesystems that
    have non-trivial directory structures.
    
    Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

Eric

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