linux-kernel - Re: [RESEND PATCH] autofs4 - remove string terminator check

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Date:	Tue, 28 Oct 2008 11:07:23 +0900
From:	Ian Kent <raven@...maw.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	autofs mailing list <autofs@...ux.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [RESEND PATCH] autofs4 - remove string terminator check

On Mon, 2008-10-27 at 18:54 -0700, Andrew Morton wrote:
> On Tue, 28 Oct 2008 10:14:30 +0900 Ian Kent <raven@...maw.net> wrote:
> 
> > In a previous patch a comment was made that checking for the existence of
> > a NULL terminator in strings copied from userspace wasn't needed as this
> > is done in many places in the kernel without problem. This patch removes
> > this string terminator check.
> > 
> 
> ah, OK.  Now I'm worried.
> 
> > 
> >  fs/autofs4/dev-ioctl.c |   20 --------------------
> >  1 files changed, 0 insertions(+), 20 deletions(-)
> > 
> > diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
> > index 625abf5..304c1ff 100644
> > --- a/fs/autofs4/dev-ioctl.c
> > +++ b/fs/autofs4/dev-ioctl.c
> > @@ -51,18 +51,6 @@ static int check_name(const char *name)
> >  }
> >  
> >  /*
> > - * Check a string doesn't overrun the chunk of
> > - * memory we copied from user land.
> > - */
> > -static int invalid_str(char *str, void *end)
> > -{
> > -	while ((void *) str <= end)
> > -		if (!*str++)
> > -			return 0;
> > -	return -EINVAL;
> > -}
> > -
> > -/*
> >   * Check that the user compiled against correct version of autofs
> >   * misc device code.
> >   *
> > @@ -143,14 +131,6 @@ static int validate_dev_ioctl(int cmd, struct autofs_dev_ioctl *param)
> >  				    cmd);
> >  			goto out;
> >  		}
> > -
> > -		err = invalid_str(param->path,
> > -				 (void *) ((size_t) param + param->size));
> > -		if (err) {
> > -			AUTOFS_WARN("invalid path supplied for cmd(0x%08x)",
> > -				    cmd);
> > -			goto out;
> > -		}
> >  	}
> >  
> >  	err = 0;
> 
> What will now happen if userspace passes in a non-null-terminated
> string (if that's possible)?
> 
> Presumably that isn't possible, or it's never been tested, because
> before we check for null-termination we run check_name(), which
> _assumes_ null-termination!
> 
> The comment over validate_dev_ioctl() will need the "and is terminated"
> removed after this change, yes?

Yes, but now I think I shouldn't have removed it.
For my part I would have been happy to keep this and now I think I
should so let's drop this patch.

Ian


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