linux-kernel - Re: [PATCH v1 2/5] relayfs: introduce dump of relayfs statistics function

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Message-Id: <20250512190427.b7fb67f6b78fd8699ea2811d@linux-foundation.org>
Date: Mon, 12 May 2025 19:04:27 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: axboe@...nel.dk, rostedt@...dmis.org, mhiramat@...nel.org,
 mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org,
 linux-block@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Jason Xing
 <kernelxing@...cent.com>, Yushan Zhou <katrinzhou@...cent.com>
Subject: Re: [PATCH v1 2/5] relayfs: introduce dump of relayfs statistics
 function

On Tue, 13 May 2025 09:48:15 +0800 Jason Xing <kerneljasonxing@...il.com> wrote:

> > > +{
> > > +     unsigned int i, full_counter = 0;
> > > +     struct rchan_buf *rbuf;
> > > +     int offset = 0;
> > > +
> > > +     if (!chan || !buf || flags & ~RELAY_DUMP_MASK)
> > > +             return;
> > > +
> > > +     if (len < RELAY_DUMP_BUF_MAX_LEN)
> > > +             return;
> >
> > So we left the memory at *buf uninitialized but failed to tell the
> > caller this.  The caller will then proceed to use uninitialized memory.
> >
> > It's a programming error, so simply going BUG seems OK.
> 
> Are you suggesting that I should remove the above check because
> developers should take care of the length of the buffer to write
> outside of the relay_dump function? or use this instead:
> WARN_ON_ONCE(len < RELAY_DUMP_BUF_MAX_LEN);
> ?

It's a poor interface - it returns uninitialized data while not
alerting the caller to this.  You'll figure something out ;)

Perhaps

	BUG_ON(len < RELAY_DUMP_BUF_MAX_LEN);
	*buf = '\0';
	if (!chan || (flags & ~RELAY_DUMP_MASK))
		return;

We don't need to check for !buf - the oops message contains the same info.

Maybe we don't need to check !chan either.  Can it be NULL here?