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

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Message-ID: <1296763614.3015.26.camel@heimdal.trondhjem.org>
Date:	Thu, 03 Feb 2011 15:06:54 -0500
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Chuck Lever <chuck.lever@...cle.com>
Cc:	Jesper Juhl <jj@...osbits.net>, 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 Thu, 2011-02-03 at 15:00 -0500, Chuck Lever wrote: 
> 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.
> 

Yes, that is guaranteed. The posix_acl structure is initialised by
posix_acl_init above, and the array itself is initialised by us in the
lines following that...

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com

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