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SubjectRe: [RFC] apparent bogosity in unregister_ftrace_function_probe_func()
On Sat, 27 Jan 2018 17:07:48 +0000
Al Viro <viro@ZenIV.linux.org.uk> wrote:

Hi Al,

> 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...

Yep, I totally agree. This code is one of those places that haven't had
the loving it deserved. It was one of our neglected children.

Thanks for taking a look here. I'm a bit embarrassed by this, and
should have audited it more. I'll have to rip into it and see what else
may be incorrect.

-- Steve

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