linux-kernel - Re: [PATCH] dax: replace sprintf() by scnprintf()

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Date:   Mon, 12 Jul 2021 09:14:53 -0700
From:   Joe Perches <joe@...ches.com>
To:     Salah Triki <salah.triki@...il.com>
Cc:     dan.j.williams@...el.com, vishal.l.verma@...el.com,
        dave.jiang@...el.com, nvdimm@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dax: replace sprintf() by scnprintf()

On Mon, 2021-07-12 at 13:26 +0100, Salah Triki wrote:
> On Sat, Jul 10, 2021 at 10:04:48AM -0700, Joe Perches wrote:
> > On Sat, 2021-07-10 at 17:46 +0100, Salah Triki wrote:
> > > Replace sprintf() by scnprintf() in order to avoid buffer overflows.
> > 
> > OK but also not strictly necessary.  DAX_NAME_LEN is 30.
> > 
> > Are you finding and changing these manually or with a script?
> > 
> > > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> > []
> > > @@ -76,7 +76,7 @@ static ssize_t do_id_store(struct device_driver *drv, const char *buf,
> > >  	fields = sscanf(buf, "dax%d.%d", &region_id, &id);
> > >  	if (fields != 2)
> > >  		return -EINVAL;
> > > -	sprintf(devname, "dax%d.%d", region_id, id);
> > > +	scnprintf(devname, DAX_NAME_LEN, "dax%d.%d", region_id, id);
> > >  	if (!sysfs_streq(buf, devname))
> > >  		return -EINVAL;
> > >  
> > > 
> > 
> > 
> 
> since region_id and id are unsigned long may be devname should be
> char[21].

I think you need to look at the code a bit more carefully.

	unsigned int region_id, id;

Also the output is %d, so the maximum length of each output
int is 10 with a possible leading minus sign.

3 + 10 + 1 + 10 + 1.  So 25 not 21 which is too small.

The %d uses could be changed to %u to make it 23.
But really it hardly matters as 30 is sufficent and the
function call depth here isn't particularly high.

> I'm finding and changing these manually.

coccinelle could help.
https://coccinelle.gitlabpages.inria.fr/website/