linux-kernel - Re: [RFC] globmatch() helper function

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Date:	Wed, 17 Dec 2008 10:47:36 -0500
From:	Steven Rostedt <srostedt@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	George Spelvin <linux@...izon.com>,
	linux-kernel@...r.kernel.org, tj@...nel.org
Subject: Re: [RFC] globmatch() helper function


On Wed, 2008-12-17 at 16:15 +0100, Peter Zijlstra wrote:
> On Wed, 2008-12-17 at 14:28 +0100, Andi Kleen wrote:
> > "George Spelvin" <linux@...izon.com> writes:
> > 
> > Wow, finally a name.
> > 
> > > 			break;
> > > 		case '*':
> > > 			if (pat[1] == '\0')	/* Optimize trailing * case */
> > > 				return true;
> > > 			/* Recurse on each possible tail of str */
> > > 			while (!globmatch(pat+1, str))
> > > 				if (!*str++)
> > > 					return false;
> > 
> > I'm uneasy with the unbounded recursion. Sure currently all the users
> > are controlled in kernel source code and expect to put in sane patterns.
> > But if someone ever adds a user controlled glob in some way it will be 
> > trivial to crash/overwrite memory with the limited kernel stack.
> > And with such a generalized function it's likely to be used more
> > in the future.
> 
> ftrace has a globbing thing in there somewhere as well and that does
> indeed take user input.
> 
> Using recursion in kernel code is indeed not recommended, what Andi said
> we have tiny stacks.

ftrace has a very limited glob feature, and requires no recursion.
Basically, we allow:

*match

match*

*match*

We do not allow match*two, that would be the same as match*

I need to look at your code (I would like a generalized glob feature for
user input). Can you accomplish the same with using a loop instead of
recursion?


-- Steve


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