RE: [PATCH] srp_daemon: Avoid extra permissions for the lock file

[Sergey Gorenko <sergeygo@nvidia.com>]

> -----Original Message-----
> From: Bart Van Assche <bvanassche@acm.org>
> Sent: Monday, September 14, 2020 7:56 PM
> To: Sergey Gorenko <sergeygo@nvidia.com>
> Cc: linux-rdma@vger.kernel.org; Max Gurtovoy <mgurtovoy@nvidia.com>
> Subject: Re: [PATCH] srp_daemon: Avoid extra permissions for the lock file
> 
> On 2020-08-19 07:17, Sergey Gorenko wrote:
> > There is no need to create a world-writable lock file.
> > It's enough to have an RW permission for the file owner only.
> >
> > Signed-off-by: Sergey Gorenko <sergeygo@nvidia.com>
> > Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > ---
> >  srp_daemon/srp_daemon.c | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/srp_daemon/srp_daemon.c b/srp_daemon/srp_daemon.c index
> > f14d9f56c9f2..fcf94537cebb 100644
> > --- a/srp_daemon/srp_daemon.c
> > +++ b/srp_daemon/srp_daemon.c
> > @@ -142,7 +142,6 @@ static int check_process_uniqueness(struct
> config_t *conf)
> >  		return -1;
> >  	}
> >
> > -	fchmod(fd,
> S_IRUSR|S_IRGRP|S_IROTH|S_IWUSR|S_IWGRP|S_IWOTH);
> >  	if (0 != lockf(fd, F_TLOCK, 0)) {
> >  		pr_err("failed to lock %s (errno: %d). possibly another "
> >  		       "srp_daemon is locking it\n", path, errno);
> 
> I think the fchmod() call was introduced by commit ee138ce1e40d ("Cause
> srp_daemon launch to fail if another srp_daemon is already working on the
> same HCA port."). Has it been verified that with this change applied that
> mechanism still works?
> 
> Anyway, please add a reference to that commit in the patch description.
> 
> Thanks,
> 
> Bart.
> 

Bart,

I tested the patch for the following scenarios:
* Start the srp_daemon service when srp_daemon is not running and the lock file does not exist.
* Start the srp_daemon service when srp_daemon is not running and the lock file exists.
* Start the srp_daemon service when srp_daemon is running and the lock file exists.
* Start the srp_daemon service when srp_daemon is running and the lock file exists and the file owner is not root. (Such scenario can happen if someone tries to run srp_daemon manually as not root. The srp_daemon fails in this case, but the lock file is created). This case is handled successfully even without the fchmod() call because the srp_daemon service starts srp_daemon as root.
 
I do not know any case when fchmod() is needed. And it does not look like a good idea to create a word-writable file owned by root. That's why I want to remove the fchmod() call.
 
Do you have an idea when the fchmod() call can be needed?
 
If you have no other objections, I will add the fixes line and send V1.

Thanks,
Sergey