linux-kernel - Re: [PATCH] nfsd: fix bad offset use

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Date:	Fri, 22 Mar 2013 14:21:13 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Zach Brown <zab@...hat.com>
Subject: Re: [PATCH] nfsd: fix bad offset use

On Fri, Mar 22, 2013 at 04:54:34PM -0400, J. Bruce Fields wrote:
> On Fri, Mar 22, 2013 at 04:53:53PM -0400, J. Bruce Fields wrote:
> > On Fri, Mar 22, 2013 at 11:18:24AM -0700, Kent Overstreet wrote:
> > > vfs_writev() updates the offset argument - but the code then passes the
> > > offset to vfs_fsync_range(). Since offset now points to the offset after
> > > what was just written, this is probably not what was intended
> > 
> > Whoops--thanks!  Looks like this was introduced by my
> > face15025ffdf664de95e86ae831544154d26c9c "nfsd: use vfs_fsync_range(),
> > not O_SYNC, for stable writes", in 3.8.
> > 
> > I'll queue up for 3.9 and stable.
> 
> (By the way, out of curiosity: how did you stumble across this?)

Just reading code - I've been trying to figure out how to improve the
way *pos pointers are passed around everywhere and I was looking at all
the users of various vfs code.

> --b.
> 
> > 
> > --b.
> > 
> > > 
> > > Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
> > > Cc: "J. Bruce Fields" <bfields@...ldses.org>
> > > Cc: Al Viro <viro@...iv.linux.org.uk>
> > > Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> > > Cc: Zach Brown <zab@...hat.com>
> > > ---
> > >  fs/nfsd/vfs.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> > > index 2a7eb53..2b2e239 100644
> > > --- a/fs/nfsd/vfs.c
> > > +++ b/fs/nfsd/vfs.c
> > > @@ -1013,6 +1013,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
> > >  	int			host_err;
> > >  	int			stable = *stablep;
> > >  	int			use_wgather;
> > > +	loff_t			pos = offset;
> > >  
> > >  	dentry = file->f_path.dentry;
> > >  	inode = dentry->d_inode;
> > > @@ -1025,7 +1026,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
> > >  
> > >  	/* Write the data. */
> > >  	oldfs = get_fs(); set_fs(KERNEL_DS);
> > > -	host_err = vfs_writev(file, (struct iovec __user *)vec, vlen, &offset);
> > > +	host_err = vfs_writev(file, (struct iovec __user *)vec, vlen, &pos);
> > >  	set_fs(oldfs);
> > >  	if (host_err < 0)
> > >  		goto out_nfserr;
> > > -- 
> > > 1.8.1.3
> > > 
--
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