Merge branch 'jk/ref-symlink-loop'

A stray symbolic link in $GIT_DIR/refs/ directory could make name
resolution loop forever, which has been corrected.

* jk/ref-symlink-loop:
  files_read_raw_ref: prevent infinite retry loops in general
  files_read_raw_ref: avoid infinite loop on broken symlinks

refs/files-backend.c

@@ -1353,6 +1353,7 @@ static int files_read_raw_ref(struct ref_store *ref_store,
 	int fd;
 	int ret = -1;
 	int save_errno;
+	int remaining_retries = 3;
 
 	*type = 0;
 	strbuf_reset(&sb_path);
@@ -1373,8 +1374,14 @@ stat_ref:
 	 * <-> symlink) between the lstat() and reading, then
 	 * we don't want to report that as an error but rather
 	 * try again starting with the lstat().
+	 *
+	 * We'll keep a count of the retries, though, just to avoid
+	 * any confusing situation sending us into an infinite loop.
 	 */
 
+	if (remaining_retries-- <= 0)
+		goto out;
+
 	if (lstat(path, &st) < 0) {
 		if (errno != ENOENT)
 			goto out;
@@ -1403,6 +1410,11 @@ stat_ref:
 			ret = 0;
 			goto out;
 		}
+		/*
+		 * It doesn't look like a refname; fall through to just
+		 * treating it like a non-symlink, and reading whatever it
+		 * points to.
+		 */
 	}
 
 	/* Is it a directory? */
@@ -1426,7 +1438,7 @@ stat_ref:
 	 */
 	fd = open(path, O_RDONLY);
 	if (fd < 0) {
-		if (errno == ENOENT)
+		if (errno == ENOENT && !S_ISLNK(st.st_mode))
 			/* inconsistent with lstat; retry */
 			goto stat_ref;
 		else

t/t1503-rev-parse-verify.sh

@@ -139,4 +139,9 @@ test_expect_success 'master@{n} for various n' '
 	test_must_fail git rev-parse --verify master@{$Np1}
 '
 
+test_expect_success SYMLINKS 'ref resolution not confused by broken symlinks' '
+	ln -s does-not-exist .git/refs/heads/broken &&
+	test_must_fail git rev-parse --verify broken
+'
+
 test_done