linux-kernel - Re: [PATCH] Fix size argument to memset call in nfsacl

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Date:	Thu, 3 Feb 2011 15:00:11 -0500
From:	Chuck Lever <chuck.lever@...cle.com>
To:	Jesper Juhl <jj@...osbits.net>
Cc:	Trond Myklebust <Trond.Myklebust@...app.com>,
	Milton Miller <miltonm@....com>, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, Neil Brown <neilb@...e.de>,
	bfields@...ldses.org
Subject: Re: [PATCH] Fix size argument to memset call in nfsacl_encode


On Feb 3, 2011, at 2:41 PM, Jesper Juhl wrote:

> On Thu, 3 Feb 2011, Trond Myklebust wrote:
> 
>> On Thu, 2011-02-03 at 20:15 +0100, Jesper Juhl wrote: 
>>> We want to give memset() the sizeof(struct posix_acl), not
>>> sizeof(struct posix_acl *).
>>> 
>>> Signed-off-by: Jesper Juhl <jj@...osbits.net>
>>> ---
>>> nfsacl.c |    2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>> 
>>> diff --git a/fs/nfs_common/nfsacl.c b/fs/nfs_common/nfsacl.c
>>> index 84c27d6..bc6d81b 100644
>>> --- a/fs/nfs_common/nfsacl.c
>>> +++ b/fs/nfs_common/nfsacl.c
>>> @@ -117,7 +117,7 @@ int nfsacl_encode(struct xdr_buf *buf, unsigned int base, struct inode *inode,
>>> 		 * invoked in contexts where a memory allocation failure is
>>> 		 * fatal.  Fortunately this fake ACL is small enough to
>>> 		 * construct on the stack. */
>>> -		memset(acl2, 0, sizeof(acl2));
>>> +		memset(acl2, 0, sizeof(*acl2));
>>> 		posix_acl_init(acl2, 4);
>>> 
>>> 		/* Insert entries in canonical order: other orders seem
>> 
>> Ccing Milton Miller who also sent in the same patch.
>> 
>> Neither patch is correct afaics. posix_acl_init() will clobber the above
>> memset, and so the correct fix is just to get rid of it...
>> 
> 
> posix_acl_init() sets a_refcount and a_count, but what about a_entries ... 
> no problem, nfsacl_encode() itself takes care of that post the 
> posix_acl_init() call.. it's all good.
> 
> So ...
> 
> 
> Remove pointless memset() in nfsacl_encode().
> 
> Thanks to Trond Myklebust <Trond.Myklebust@...app.com> for pointing out 
> that it is not needed since posix_acl_init() will set everything 
> regardless..
> 
> Signed-off-by: Jesper Juhl <jj@...osbits.net>
> ---
> nfsacl.c |    1 -
> 1 file changed, 1 deletion(-)
> 
> diff --git a/fs/nfs_common/nfsacl.c b/fs/nfs_common/nfsacl.c
> index 84c27d6..ec0f277 100644
> --- a/fs/nfs_common/nfsacl.c
> +++ b/fs/nfs_common/nfsacl.c
> @@ -117,7 +117,6 @@ int nfsacl_encode(struct xdr_buf *buf, unsigned int base, struct inode *inode,
> 		 * invoked in contexts where a memory allocation failure is
> 		 * fatal.  Fortunately this fake ACL is small enough to
> 		 * construct on the stack. */
> -		memset(acl2, 0, sizeof(acl2));
> 		posix_acl_init(acl2, 4);
> 
> 		/* Insert entries in canonical order: other orders seem

If there is a guarantee that random data that potentially resides between the fields in that structure will never appear on the wire, then ACK.

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com




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