Re: [PATCH 5/6] fuse: truncate file if async dio failed

[Maxim V. Patlasov]

Hi,

12/15/2012 12:16 AM, Brian Foster ÐÐÑÐÑ:
> On 12/14/2012 10:21 AM, Maxim V. Patlasov wrote:
> > The patch improves error handling in fuse_direct_IO(): if we successfully
> > submitted several fuse requests on behalf of synchronous direct write
> > extending file and some of them failed, let's try to do our best to clean-up.
> >
> > Signed-off-by: Maxim Patlasov <mpatlasov@xxxxxxxxxxxxx>
> > ---
> >   fs/fuse/file.c |   55 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
> >   1 files changed, 53 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > index 05eed23..b6e9b8d 100644
> > --- a/fs/fuse/file.c
> > +++ b/fs/fuse/file.c
> > @@ -2340,6 +2340,53 @@ int fuse_notify_poll_wakeup(struct fuse_conn *fc,
> >   	return 0;
> >   }
> >   
> > +static void fuse_do_truncate(struct file *file)
> > +{
> > +	struct fuse_file *ff = file->private_data;
> > +	struct inode *inode = file->f_mapping->host;
> > +	struct fuse_conn *fc = get_fuse_conn(inode);
> > +	struct fuse_req *req;
> > +	struct fuse_setattr_in inarg;
> > +	struct fuse_attr_out outarg;
> > +	int err;
> > +
> > +	req = fuse_get_req_nopages(fc);
> > +	if (IS_ERR(req)) {
> > +		printk(KERN_WARNING "failed to allocate req for truncate "
> > +		       "(%ld)\n", PTR_ERR(req));
> > +		return;
> > +	}
> > +
> > +	memset(&inarg, 0, sizeof(inarg));
> > +	memset(&outarg, 0, sizeof(outarg));
> > +
> > +	inarg.valid |= FATTR_SIZE;
> > +	inarg.size = i_size_read(inode);
> > +
> > +	inarg.valid |= FATTR_FH;
> > +	inarg.fh = ff->fh;
> > +
> > +	req->in.h.opcode = FUSE_SETATTR;
> > +	req->in.h.nodeid = get_node_id(inode);
> > +	req->in.numargs = 1;
> > +	req->in.args[0].size = sizeof(inarg);
> > +	req->in.args[0].value = &inarg;
> > +	req->out.numargs = 1;
> > +	if (fc->minor < 9)
> > +		req->out.args[0].size = FUSE_COMPAT_ATTR_OUT_SIZE;
> > +	else
> > +		req->out.args[0].size = sizeof(outarg);
> > +	req->out.args[0].value = &outarg;
> > +
> > +	fuse_request_send(fc, req);
> > +	err = req->out.h.error;
> > +	fuse_put_request(fc, req);
> > +
> > +	if (err)
> > +		printk(KERN_WARNING "failed to truncate to %lld with error "
> > +		       "%d\n", i_size_read(inode), err);
> > +}
> > +
> fuse_do_truncate() looks fairly close to fuse_do_setattr(). Is there any
> reason we couldn't make fuse_do_setattr() non-static, change the dentry
> parameter to an inode and use that?

fuse_do_setattr() performs extra checks that fuse_do_truncate() needn't. 
Some of them are harmless, some not: fuse_allow_task() may return 0 if 
task credentials changed. E.g. super-user successfully opened a file, 
then setuid(other_user_uid), then write(2) to the file. write(2) doesn't 
check uid, but fuse_do_truncate() - via fuse_allow_task() - does.

This non-POSIX behaviour (ftruncate(2) returning -1 with errno==EACCES) 
was introduced long time ago:

> commit e57ac68378a287d6336d187b26971f35f7ee7251
> Author: Miklos Szeredi <mszeredi@xxxxxxx>
> Date:   Thu Oct 18 03:06:58 2007 -0700
>
>     fuse: fix allowing operations
>
>     The following operation didn't check if sending the request was 
> allowed:
>
>       setattr
>       listxattr
>       statfs
>
>     Some other operations don't explicitly do the check, but VFS calls
>     ->permission() which checks this.
>
>     Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
>     Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>     Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

and I'm not sure whether it was done intentionally or not. Maybe Miklos 
could shed some light on it...

Thanks,
Maxim
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