Fix memory leak in String#start_with? when regexp times out

[Bug #20653]

This commit refactors how Onigmo handles timeout. Instead of raising a
timeout error, onig_search will return a ONIGERR_TIMEOUT which the
caller can free memory, and then raise a timeout error.

This fixes a memory leak in String#start_with when the regexp times out.
For example:

    regex = Regexp.new("^#{"(a*)" * 10_000}x$", timeout: 0.000001)
    str = "a" * 1000000 + "x"

    10.times do
      100.times do
        str.start_with?(regex)
      rescue
      end

      puts `ps -o rss= -p #{$$}`
    end

Before:

    33216
    51936
    71152
    81728
    97152
    103248
    120384
    133392
    133520
    133616

After:

    14912
    15376
    15824
    15824
    16128
    16128
    16144
    16144
    16160
    16160

re.c

@@ -1719,12 +1719,18 @@ rb_reg_onig_match(VALUE re, VALUE str,
     if (result < 0) {
         onig_region_free(regs, 0);
 
-        if (result != ONIG_MISMATCH) {
+        switch (result) {
+          case ONIG_MISMATCH:
+            break;
+          case ONIGERR_TIMEOUT:
+            rb_raise(rb_eRegexpTimeoutError, "regexp match timeout");
+          default: {
             onig_errmsg_buffer err = "";
             onig_error_code_to_str((UChar*)err, (int)result);
             rb_reg_raise(err, re);
           }
         }
+    }
 
     return result;
 }
@@ -1783,23 +1789,6 @@ reg_onig_search(regex_t *reg, VALUE str, struct re_registers *regs, void *args_p
         ONIG_OPTION_NONE);
 }
 
-struct rb_reg_onig_match_args {
-    VALUE re;
-    VALUE str;
-    struct reg_onig_search_args args;
-    struct re_registers regs;
-
-    OnigPosition result;
-};
-
-static VALUE
-rb_reg_onig_match_try(VALUE value_args)
-{
-    struct rb_reg_onig_match_args *args = (struct rb_reg_onig_match_args *)value_args;
-    args->result = rb_reg_onig_match(args->re, args->str, reg_onig_search, &args->args, &args->regs);
-    return Qnil;
-}
-
 /* returns byte offset */
 static long
 rb_reg_search_set_match(VALUE re, VALUE str, long pos, int reverse, int set_backref_str, VALUE *set_match)
@@ -1810,38 +1799,22 @@ rb_reg_search_set_match(VALUE re, VALUE str, long pos, int reverse, int set_back
         return -1;
     }
 
-    struct rb_reg_onig_match_args args = {
-        .re = re,
-        .str = str,
-        .args = {
+    struct reg_onig_search_args args = {
         .pos = pos,
         .range = reverse ? 0 : len,
-        },
-        .regs = {0}
     };
+    struct re_registers regs = {0};
 
-    /* If there is a timeout set, then rb_reg_onig_match could raise a
-     * Regexp::TimeoutError so we want to protect it from leaking memory. */
-    if (rb_reg_match_time_limit) {
-        int state;
-        rb_protect(rb_reg_onig_match_try, (VALUE)&args, &state);
-        if (state) {
-            onig_region_free(&args.regs, false);
-            rb_jump_tag(state);
-        }
-    }
-    else {
-        rb_reg_onig_match_try((VALUE)&args);
-    }
+    OnigPosition result = rb_reg_onig_match(re, str, reg_onig_search, &args, &regs);
 
-    if (args.result == ONIG_MISMATCH) {
+    if (result == ONIG_MISMATCH) {
         rb_backref_set(Qnil);
         return ONIG_MISMATCH;
     }
 
     VALUE match = match_alloc(rb_cMatch);
     rb_matchext_t *rm = RMATCH_EXT(match);
-    rm->regs = args.regs;
+    rm->regs = regs;
 
     if (set_backref_str) {
         RB_OBJ_WRITE(match, &RMATCH(match)->str, rb_str_new4(str));
@@ -1858,7 +1831,7 @@ rb_reg_search_set_match(VALUE re, VALUE str, long pos, int reverse, int set_back
     rb_backref_set(match);
     if (set_match) *set_match = match;
 
-    return args.result;
+    return result;
 }
 
 long
@@ -4720,12 +4693,6 @@ rb_reg_timeout_p(regex_t *reg, void *end_time_)
     return false;
 }
 
-void
-rb_reg_raise_timeout(void)
-{
-    rb_raise(rb_eRegexpTimeoutError, "regexp match timeout");
-}
-
 /*
  *  call-seq:
  *     Regexp.timeout  -> float or nil

regexec.c

@@ -5575,8 +5575,7 @@ onig_search_gpos(regex_t* reg, const UChar* str, const UChar* end,
 
 timeout:
   MATCH_ARG_FREE(msa);
-  onig_region_free(region, false);
-  HANDLE_REG_TIMEOUT_IN_MATCH_AT;
+  return ONIGERR_TIMEOUT;
 }
 
 extern OnigPosition

regint.h

@@ -163,9 +163,6 @@
     rb_thread_check_ints(); \
   } \
 } while(0)
-# define HANDLE_REG_TIMEOUT_IN_MATCH_AT do { \
-  rb_reg_raise_timeout(); \
-} while (0)
 # define onig_st_init_table                  st_init_table
 # define onig_st_init_table_with_size        st_init_table_with_size
 # define onig_st_init_numtable               st_init_numtable
@@ -1002,7 +999,6 @@ extern int onig_st_insert_strend(hash_table_type* table, const UChar* str_key, c
 extern size_t onig_memsize(const regex_t *reg);
 extern size_t onig_region_memsize(const struct re_registers *regs);
 bool rb_reg_timeout_p(regex_t *reg, void *end_time);
-NORETURN(void rb_reg_raise_timeout(void));
 #endif
 
 RUBY_SYMBOL_EXPORT_END

test/ruby/test_string.rb

@@ -1971,6 +1971,22 @@ CODE
     assert_nil($&)
   end
 
+  def test_start_with_timeout_memory_leak
+    assert_no_memory_leak([], "#{<<~"begin;"}", "#{<<~'end;'}", "[Bug #20653]", rss: true)
+      regex = Regexp.new("^#{"(a*)" * 10_000}x$", timeout: 0.000001)
+      str = "a" * 1_000_000 + "x"
+
+      code = proc do
+        str.start_with?(regex)
+      rescue
+      end
+
+      10.times(&code)
+    begin;
+      1_000.times(&code)
+    end;
+  end
+
   def test_strip
     assert_equal(S("x"), S("      x        ").strip)
     assert_equal(S("x"), S(" \n\r\t     x  \t\r\n\n      ").strip)