linux-kernel - Re: [PATCH 1/2] raw: test against runtime value of max_raw

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Date:	Tue, 04 Feb 2014 23:50:18 +0100
From:	Paul Bolle <pebolle@...cali.nl>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jan Kara <jack@...e.cz>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] raw: test against runtime value of max_raw_minors

[Added Jan Kara.]

On Tue, 2014-02-04 at 14:34 -0800, Greg Kroah-Hartman wrote:
> On Tue, Feb 04, 2014 at 11:23:12PM +0100, Paul Bolle wrote:
> > bind_get() checks the device number it is called with. It uses
> > MAX_RAW_MINORS for the upper bound. But MAX_RAW_MINORS is set at compile
> > time while the actual number of raw devices can be set at runtime. This
> > means the test can either be too strict or too lenient. And if the test
> > ends up being too lenient bind_get() might try to access memory beyond
> > what was allocated for "raw_devices".
> > 
> > So check against the runtime value (max_raw_minors) in this function.
> > 
> > Signed-off-by: Paul Bolle <pebolle@...cali.nl>
> > ---
> >  drivers/char/raw.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/char/raw.c b/drivers/char/raw.c
> > index f3223aa..6e8d65e 100644
> > --- a/drivers/char/raw.c
> > +++ b/drivers/char/raw.c
> > @@ -190,7 +190,7 @@ static int bind_get(int number, dev_t *dev)
> >  	struct raw_device_data *rawdev;
> >  	struct block_device *bdev;
> >  
> > -	if (number <= 0 || number >= MAX_RAW_MINORS)
> > +	if (number <= 0 || number >= max_raw_minors)
> 
> Are you sure?  For some reason, I thought this was changed to be this
> way a long time ago, can you please dig through the git archives, and
> even the history.git tree, to verify that this is correct and you aren't
> just making this be as it was before?

What apparently happened was that in v3.0, through commit 0078bff5283d
("Allow setting of number of raw devices as a module parameter"), the
test in bind_set() was updated but the test in bind_get() not.

You can - sort of - see this by comparing
    git grep -nwi max_raw_minors 0078bff5283d^

and
    git grep -nwi max_raw_minors 0078bff5283d

 

Paul Bolle

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