merge revision(s) abc0304cb28cb9dcc3476993bc487884c139fd11: [Backport #17507]

	Avoid race condition in Regexp#match

	In certain conditions, Regexp#match could return a MatchData with
	missing captures.  This seems to require at the least, multiple
	threads calling a method that calls the same block/proc/lambda
	which calls Regexp#match.

	The race condition happens because the MatchData is passed from
	indirectly via the backref, and other threads can modify the
	backref.

	Fix the issue by:

	1. Not reusing the existing MatchData from the backref, and always
	   allocating a new MatchData.
	2. Passing the MatchData directly to the caller using a VALUE*,
	   instead of indirectly through the backref.

	It's likely that variants of this issue exist for other Regexp
	methods.  Anywhere that MatchData is passed implicitly through
	the backref is probably vulnerable to this issue.

	Fixes [Bug #17507]
	---
	 re.c                     | 46 +++++++++++++++++++---------------------------
	 test/ruby/test_regexp.rb | 21 +++++++++++++++++++++
	 2 files changed, 40 insertions(+), 27 deletions(-)

1 files changed, 19 insertions, 27 deletions

diff --git a/re.c b/re.c
index f3e8954185..5b6f129963 100644
--- a/re.c
+++ b/re.c
@@ -1546,8 +1546,8 @@ rb_reg_adjust_startpos(VALUE re, VALUE str, long pos, int reverse)
 }
 
 /* returns byte offset */
-long
-rb_reg_search0(VALUE re, VALUE str, long pos, int reverse, int set_backref_str)
+static long
+rb_reg_search_set_match(VALUE re, VALUE str, long pos, int reverse, int set_backref_str, VALUE *set_match)
 {
     long result;
     VALUE match;
@@ -1569,18 +1569,7 @@ rb_reg_search0(VALUE re, VALUE str, long pos, int reverse, int set_backref_str)
     tmpreg = reg != RREGEXP_PTR(re);
     if (!tmpreg) RREGEXP(re)->usecnt++;
 
-    match = rb_backref_get();
-    if (!NIL_P(match)) {
-	if (FL_TEST(match, MATCH_BUSY)) {
-	    match = Qnil;
-	}
-	else {
-	    regs = RMATCH_REGS(match);
-	}
-    }
-    if (NIL_P(match)) {
-	MEMZERO(regs, struct re_registers, 1);
-    }
+    MEMZERO(regs, struct re_registers, 1);
     if (!reverse) {
 	range += len;
     }
@@ -1613,13 +1602,10 @@ rb_reg_search0(VALUE re, VALUE str, long pos, int reverse, int set_backref_str)
 	}
     }
 
-    if (NIL_P(match)) {
-	int err;
-	match = match_alloc(rb_cMatch);
-	err = rb_reg_region_copy(RMATCH_REGS(match), regs);
-	onig_region_free(regs, 0);
-	if (err) rb_memerror();
-    }
+    match = match_alloc(rb_cMatch);
+    int copy_err = rb_reg_region_copy(RMATCH_REGS(match), regs);
+    onig_region_free(regs, 0);
+    if (copy_err) rb_memerror();
 
     if (set_backref_str) {
 	RMATCH(match)->str = rb_str_new4(str);
@@ -1627,11 +1613,18 @@ rb_reg_search0(VALUE re, VALUE str, long pos, int reverse, int set_backref_str)
 
     RMATCH(match)->regexp = re;
     rb_backref_set(match);
+    if (set_match) *set_match = match;
 
     return result;
 }
 
 long
+rb_reg_search0(VALUE re, VALUE str, long pos, int reverse, int set_backref_str)
+{
+    return rb_reg_search_set_match(re, str, pos, reverse, set_backref_str, NULL);
+}
+
+long
 rb_reg_search(VALUE re, VALUE str, long pos, int reverse)
 {
     return rb_reg_search0(re, str, pos, reverse, 1);
@@ -3127,7 +3120,7 @@ reg_operand(VALUE s, int check)
 }
 
 static long
-reg_match_pos(VALUE re, VALUE *strp, long pos)
+reg_match_pos(VALUE re, VALUE *strp, long pos, VALUE* set_match)
 {
     VALUE str = *strp;
 
@@ -3146,7 +3139,7 @@ reg_match_pos(VALUE re, VALUE *strp, long pos)
 	}
 	pos = rb_str_offset(str, pos);
     }
-    return rb_reg_search(re, str, pos, 0);
+    return rb_reg_search_set_match(re, str, pos, 0, 1, set_match);
 }
 
 /*
@@ -3200,7 +3193,7 @@ reg_match_pos(VALUE re, VALUE *strp, long pos)
 VALUE
 rb_reg_match(VALUE re, VALUE str)
 {
-    long pos = reg_match_pos(re, &str, 0);
+    long pos = reg_match_pos(re, &str, 0, NULL);
     if (pos < 0) return Qnil;
     pos = rb_str_sublen(str, pos);
     return LONG2FIX(pos);
@@ -3311,7 +3304,7 @@ rb_reg_match2(VALUE re)
 static VALUE
 rb_reg_match_m(int argc, VALUE *argv, VALUE re)
 {
-    VALUE result, str, initpos;
+    VALUE result = Qnil, str, initpos;
     long pos;
 
     if (rb_scan_args(argc, argv, "11", &str, &initpos) == 2) {
@@ -3321,12 +3314,11 @@ rb_reg_match_m(int argc, VALUE *argv, VALUE re)
 	pos = 0;
     }
 
-    pos = reg_match_pos(re, &str, pos);
+    pos = reg_match_pos(re, &str, pos, &result);
     if (pos < 0) {
 	rb_backref_set(Qnil);
 	return Qnil;
     }
-    result = rb_backref_get();
     rb_match_busy(result);
     if (!NIL_P(result) && rb_block_given_p()) {
 	return rb_yield(result);