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SubjectRe: [RFC] apparent bogosity in unregister_ftrace_function_probe_func()
2018-02-05 22:54 GMT+00:00 Steven Rostedt <rostedt@goodmis.org>:
> On Mon, 29 Jan 2018 22:59:42 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
>> On Sat, 27 Jan 2018 17:07:48 +0000
>> Al Viro <viro@ZenIV.linux.org.uk> wrote:
>>
>> > 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.
>>
>> Looks nice to me!
>>
>
> I'll implement this code giving Al credit and referencing this email
> thread. Anyone have objections to that?

Thank you, Steven.
No objections from me.

--
Dmitry

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