fsck: use strbuf_getline() to read skiplist file

The buffer is unlikely to contain a NUL character, so printing its
contents using %s in a die() format is unsafe (detected with ASan).

Use an idiomatic strbuf_getline() loop instead, which ensures the buffer
is always NUL-terminated, supports CRLF files as well, accepts files
without a newline after the last line, supports any hash length
automatically, and is shorter.

This fixes a bug where emitting an error about an invalid line on say
line 1 would continue printing subsequent lines, and usually continue
into uninitialized memory.

The performance impact of this, on a CentOS 7 box with RedHat GCC
4.8.5-28:

    $ GIT_PERF_REPEAT_COUNT=5 GIT_PERF_MAKE_OPTS='-j56 CFLAGS="-O3"' ./run HEAD~ HEAD p1451-fsck-skip-list.sh
    Test                                             HEAD~             HEAD
    ----------------------------------------------------------------------------------------
    1450.3: fsck with 0 skipped bad commits          7.75(7.39+0.35)   7.68(7.29+0.39) -0.9%
    1450.5: fsck with 1 skipped bad commits          7.70(7.30+0.40)   7.80(7.42+0.37) +1.3%
    1450.7: fsck with 10 skipped bad commits         7.77(7.37+0.40)   7.87(7.47+0.40) +1.3%
    1450.9: fsck with 100 skipped bad commits        7.82(7.41+0.40)   7.88(7.43+0.44) +0.8%
    1450.11: fsck with 1000 skipped bad commits      7.88(7.49+0.39)   7.84(7.43+0.40) -0.5%
    1450.13: fsck with 10000 skipped bad commits     8.02(7.63+0.39)   8.07(7.67+0.39) +0.6%
    1450.15: fsck with 100000 skipped bad commits    8.01(7.60+0.41)   8.08(7.70+0.38) +0.9%
    1450.17: fsck with 1000000 skipped bad commits   7.60(7.10+0.50)   7.37(7.18+0.19) -3.0%

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 13 insertions, 14 deletions

diff --git a/fsck.c b/fsck.c
index a0cee0be59..972a26b9ba 100644
--- a/fsck.c
+++ b/fsck.c
@@ -183,8 +183,9 @@ static int fsck_msg_type(enum fsck_msg_id msg_id,
 static void init_skiplist(struct fsck_options *options, const char *path)
 {
 	static struct oid_array skiplist = OID_ARRAY_INIT;
-	int sorted, fd;
-	char buffer[GIT_MAX_HEXSZ + 1];
+	int sorted;
+	FILE *fp;
+	struct strbuf sb = STRBUF_INIT;
 	struct object_id oid;
 
 	if (options->skiplist)
@@ -194,25 +195,23 @@ static void init_skiplist(struct fsck_options *options, const char *path)
 		options->skiplist = &skiplist;
 	}
 
-	fd = open(path, O_RDONLY);
-	if (fd < 0)
+	fp = fopen(path, "r");
+	if (!fp)
 		die("Could not open skip list: %s", path);
-	for (;;) {
+	while (!strbuf_getline(&sb, fp)) {
 		const char *p;
-		int result = read_in_full(fd, buffer, sizeof(buffer));
-		if (result < 0)
-			die_errno("Could not read '%s'", path);
-		if (!result)
-			break;
-		if (parse_oid_hex(buffer, &oid, &p) || *p != '\n')
-			die("Invalid SHA-1: %s", buffer);
+		if (parse_oid_hex(sb.buf, &oid, &p) || *p != '\0')
+			die("Invalid SHA-1: %s", sb.buf);
 		oid_array_append(&skiplist, &oid);
 		if (sorted && skiplist.nr > 1 &&
 				oidcmp(&skiplist.oid[skiplist.nr - 2],
 				       &oid) > 0)
 			sorted = 0;
 	}
-	close(fd);
+	if (ferror(fp))
+		die_errno("Could not read '%s'", path);
+	fclose(fp);
+	strbuf_release(&sb);
 
 	if (sorted)
 		skiplist.sorted = 1;
diff --git a/t/t5504-fetch-receive-strict.sh b/t/t5504-fetch-receive-strict.sh
index 96bf9facbd..d67ab37321 100755
--- a/t/t5504-fetch-receive-strict.sh
+++ b/t/t5504-fetch-receive-strict.sh
@@ -185,7 +185,7 @@ test_expect_success 'fsck with invalid or bogus skipList input (comments & empty
 	test_i18ngrep "^fatal: Invalid SHA-1: " err-with-empty-line
 '
 
-test_expect_failure 'fsck no garbage output from comments & empty lines errors' '
+test_expect_success 'fsck no garbage output from comments & empty lines errors' '
 	test_line_count = 1 err-with-comment &&
 	test_line_count = 1 err-with-empty-line
 '