[PATCH 2/2] resolve_ref_unsafe(): limit the number of "stat_ref" retries

[Petr Stodulka <pstodulk@redhat.com>]

From: Michael Haggerty <mhagger@alum.mit.edu>

If there is a broken symlink where a loose reference file is expected,
then the attempt to open() it fails with ENOENT. This error is
misinterpreted to mean that the loose reference file itself has
disappeared due to a race, causing the lookup to be retried. But in
this scenario, the retries all suffer from the same problem, causing
an infinite loop.

So put a limit (of 5) on the number of times that the stat_ref step
can be retried.

Based-on-patch-by: Petr Stodulka <pstodulk@redhat.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 refs/files-backend.c | 6 ++++--
 refs/refs-internal.h | 6 ++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/refs/files-backend.c b/refs/files-backend.c
index d16feb1..245a0b5 100644
--- a/refs/files-backend.c
+++ b/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 retries = 0;
 
 	*type = 0;
 	strbuf_reset(&sb_path);
@@ -1390,7 +1391,8 @@ static int files_read_raw_ref(struct ref_store *ref_store,
 	if (S_ISLNK(st.st_mode)) {
 		strbuf_reset(&sb_contents);
 		if (strbuf_readlink(&sb_contents, path, 0) < 0) {
-			if (errno == ENOENT || errno == EINVAL)
+			if ((errno == ENOENT || errno == EINVAL) &&
+				retries++ < MAXRETRIES) 
 				/* inconsistent with lstat; retry */
 				goto stat_ref;
 			else
@@ -1426,7 +1428,7 @@ static int files_read_raw_ref(struct ref_store *ref_store,
 	 */
 	fd = open(path, O_RDONLY);
 	if (fd < 0) {
-		if (errno == ENOENT)
+		if (errno == ENOENT && retries++ < MAXRETRIES)
 			/* inconsistent with lstat; retry */
 			goto stat_ref;
 		else
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 708b260..37e6b99 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -255,6 +255,12 @@ int rename_ref_available(const char *old_refname, const char *new_refname);
 /* We allow "recursive" symbolic refs. Only within reason, though */
 #define SYMREF_MAXDEPTH 5
 
+/* 
+ * We allow only MAXRETRIES tries to jump on stat_ref, because of possible
+ * infinite loop
+ */
+#define MAXRETRIES 5
+
 /* Include broken references in a do_for_each_ref*() iteration: */
 #define DO_FOR_EACH_INCLUDE_BROKEN 0x01
 
-- 
2.5.5