linux-kernel - Re: [PATCH v5 5/7] blktrace: fix debugfs use after free

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Message-ID: <20200605223320.GN11244@42.do-not-panic.com>
Date:   Fri, 5 Jun 2020 22:33:20 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     Christoph Hellwig <hch@...radead.org>, axboe@...nel.dk,
        viro@...iv.linux.org.uk, gregkh@...uxfoundation.org,
        rostedt@...dmis.org, mingo@...hat.com, jack@...e.cz,
        ming.lei@...hat.com, nstange@...e.de, akpm@...ux-foundation.org,
        mhocko@...e.com, yukuai3@...wei.com, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Omar Sandoval <osandov@...com>,
        Hannes Reinecke <hare@...e.com>,
        Michal Hocko <mhocko@...nel.org>,
        syzbot+603294af2d01acfdd6da@...kaller.appspotmail.com
Subject: Re: [PATCH v5 5/7] blktrace: fix debugfs use after free

On Thu, Jun 04, 2020 at 09:48:43PM -0700, Bart Van Assche wrote:
> On 2020-06-01 10:05, Luis Chamberlain wrote:
> > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> > index a55cbfd060f5..5b0310f38e11 100644
> > --- a/kernel/trace/blktrace.c
> > +++ b/kernel/trace/blktrace.c
> > @@ -511,6 +511,11 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
> >  	 */
> >  	if (bdev && bdev != bdev->bd_contains) {
> >  		dir = bdev->bd_part->debugfs_dir;
> > +	} else if (q->sg_debugfs_dir &&
> > +		   strlen(buts->name) == strlen(q->sg_debugfs_dir->d_name.name)
> > +		   && strcmp(buts->name, q->sg_debugfs_dir->d_name.name) == 0) {
> > +		/* scsi-generic requires use of its own directory */
> > +		dir = q->sg_debugfs_dir;
> >  	} else {
> >  		/*
> >  		 * For queues that do not have a gendisk attached to them, that
> > 
> 
> Please Cc Martin Petersen for patches that modify SCSI code.

Sure thing.
> The string comparison check looks fragile to me. Is the purpose of that

> check perhaps to verify whether tracing is being activated through the
> SCSI generic interface?

Yes.

> If so, how about changing that test into
> something like the following?
> 
> 	MAJOR(dev) == SCSI_GENERIC_MAJOR

Sure.

  Luis