linux-kernel - Re: [RFC] apparent bogosity in unregister_ftrace_function_probe

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Date:   Sat, 27 Jan 2018 17:07:48 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Dmitry Safonov <0x7f454c46@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] apparent bogosity in
 unregister_ftrace_function_probe_func()

On Sat, Jan 27, 2018 at 01:59:56PM +0000, Dmitry Safonov wrote:
> 
> > Incidentally, shouldn't filter_parse_regex("*[ab]", 5, &s, &not)
> > end up with s = "*[ab]"?  We are returning MATCH_GLOB, after all,
> > so we want the entire pattern there...  I would've assumed that
> > this is what the code in unregister_ftrace_function_probe_func()
> > is trying to compensate for, the first oddity predates MATCH_GLOB...
> 
> No, I don't think filter_parse_regex() should return the full regex..
> ftrace_match() expects search would be processed string, not a glob.
> So, this unnecessary assignment broke unregistering multiple kprobs
> with a middle/end pattern..

For substring - sure, but what about something like "*a*b" and "a*b"?
AFAICS, filter_parse_regex() ends up with identical results in both
cases - MATCH_GLOB and *search = "a*b".  And no way for the caller
to tell one from another.

IOW, it's a different bug sometimes obscured by the one in
unregister_ftrace_function_probe_func().  filter_parse_regex()
ought to revert to *search = buff; when it decides to return
MATCH_GLOB.  Or something like
        for (i = 0; i < len; i++) {
                if (buff[i] == '*') {
                        if (!i) {
                                type = MATCH_END_ONLY;
                        } else if (i == len - 1) {
                                if (type == MATCH_END_ONLY)
                                        type = MATCH_MIDDLE_ONLY;
                                else
                                        type = MATCH_FRONT_ONLY;
                                buff[i] = 0;
                                break;
                        } else {        /* pattern continues, use full glob */
                                return MATCH_GLOB;
                        }
                } else if (strchr("[?\\", buff[i])) {
                        return MATCH_GLOB;
                }
        }
        if (buff[0] == '*')
                *search = buff + 1;
for that matter - i.e. delay that "we want everything past the first character"
until we are certain it's not a MATCH_GLOB.

That one was introduced by "ftrace: Support full glob matching" in 2016, AFAICS...