[PATCH 2/2] grep: fix segfault under -P + PCRE2 + (*NO_JIT)

[Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>]

Fix a bug in the compilation of PCRE2 patterns under JIT (the most
common runtime configuration), any pattern with a (*NO_JIT) verb would
segfault. This bug dates back to my 94da9193a6 ("grep: add support for
PCRE v2", 2017-06-01):

    $ git grep -P '(*NO_JIT)hi.*there'
    Segmentation fault

As explained ad more length in the comment being added here it isn't
sufficient to just check pcre2_config() to see whether the JIT should
be used, pcre2_pattern_info() also has to be asked.

This is something I discovered myself when fiddling around with PCRE2
verbs in patterns passed to git. I don't expect that any user of git
has encountered this given the obscurity of passing PCRE2 verbs
through to the library, along with the relative obscurity of (*NO_JIT)
itself.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
---
 grep.c          | 25 +++++++++++++++++++++++++
 t/t7810-grep.sh |  6 ++++++
 2 files changed, 31 insertions(+)

diff --git a/grep.c b/grep.c
index d0b9b6cdfa..f3139e867c 100644
--- a/grep.c
+++ b/grep.c
@@ -477,6 +477,8 @@ static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt
 	int options = PCRE2_MULTILINE;
 	const uint8_t *character_tables = NULL;
 	int jitret;
+	int patinforet;
+	size_t jitsizearg;
 
 	assert(opt->pcre2);
 
@@ -511,6 +513,29 @@ static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt
 		jitret = pcre2_jit_compile(p->pcre2_pattern, PCRE2_JIT_COMPLETE);
 		if (jitret)
 			die("Couldn't JIT the PCRE2 pattern '%s', got '%d'\n", p->pattern, jitret);
+
+		/*
+		 * The pcre2_config(PCRE2_CONFIG_JIT, ...) call just
+		 * tells us whether the library itself supports JIT,
+		 * but to see whether we're going to be actually using
+		 * JIT we need to extract PCRE2_INFO_JITSIZE from the
+		 * pattern *after* we do pcre2_jit_compile() above.
+		 *
+		 * This is because if the pattern contains the
+		 * (*NO_JIT) verb (see pcre2syntax(3))
+		 * pcre2_jit_compile() will exit early with 0. If we
+		 * then proceed to call pcre2_jit_match() further down
+		 * the line instead of pcre2_match() we'll segfault.
+		 */
+		patinforet = pcre2_pattern_info(p->pcre2_pattern, PCRE2_INFO_JITSIZE, &jitsizearg);
+		if (patinforet)
+			die("BUG: The patinforet variable should be 0 after the pcre2_pattern_info() call, not %d",
+			    patinforet);
+		if (jitsizearg == 0) {
+			p->pcre2_jit_on = 0;
+			return;
+		}
+
 		p->pcre2_jit_stack = pcre2_jit_stack_create(1, 1024 * 1024, NULL);
 		if (!p->pcre2_jit_stack)
 			die("Couldn't allocate PCRE2 JIT stack");
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index 2a6679c2f5..c8ff50cc30 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -1110,6 +1110,12 @@ test_expect_success PCRE 'grep -P pattern' '
 	test_cmp expected actual
 '
 
+test_expect_success LIBPCRE2 "grep -P with (*NO_JIT) doesn't error out" '
+	git grep -P "(*NO_JIT)\p{Ps}.*?\p{Pe}" hello.c >actual &&
+	test_cmp expected actual
+
+'
+
 test_expect_success !PCRE 'grep -P pattern errors without PCRE' '
 	test_must_fail git grep -P "foo.*bar"
 '
-- 
2.15.0.403.gc27cc4dac6