[RFC][PATCH 2/6] tracing: Fix parsing of globs with a wildcard at the beginning

[Steven Rostedt <rostedt@goodmis.org>]

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From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Al Viro reported:

    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.

Testing this with the following:

 # cd /sys/kernel/tracing
 # echo '*raw*lock' > set_ftrace_filter
 bash: echo: write error: Invalid argument

With this patch:

 # echo '*raw*lock' > set_ftrace_filter
 # cat set_ftrace_filter
_raw_read_trylock
_raw_write_trylock
_raw_read_unlock
_raw_spin_unlock
_raw_write_unlock
_raw_spin_trylock
_raw_spin_lock
_raw_write_lock
_raw_read_lock

Al recommended not setting the search buffer to skip the first '*' unless we
know we are not using MATCH_GLOB. This implements his suggested logic.

Link: http://lkml.kernel.org/r/20180127170748.GF13338@ZenIV.linux.org.uk

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 60f1d5e3bac44 ("ftrace: Support full glob matching")
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Suggsted-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_events_filter.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 61e7f0678d33..a764aec3c9a1 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -400,7 +400,6 @@ enum regex_type filter_parse_regex(char *buff, int len, char **search, int *not)
 	for (i = 0; i < len; i++) {
 		if (buff[i] == '*') {
 			if (!i) {
-				*search = buff + 1;
 				type = MATCH_END_ONLY;
 			} else if (i == len - 1) {
 				if (type == MATCH_END_ONLY)
@@ -410,14 +409,14 @@ enum regex_type filter_parse_regex(char *buff, int len, char **search, int *not)
 				buff[i] = 0;
 				break;
 			} else {	/* pattern continues, use full glob */
-				type = MATCH_GLOB;
-				break;
+				return MATCH_GLOB;
 			}
 		} else if (strchr("[?\\", buff[i])) {
-			type = MATCH_GLOB;
-			break;
+			return MATCH_GLOB;
 		}
 	}
+	if (buff[0] == '*')
+		*search = buff + 1;
 
 	return type;
 }
-- 
2.15.1