[PATCH] unpack_entry: invalidate newly added cache entry in case of error

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

In this particular code path, we add "base" to the delta base
cache. Then decide to free it, but we forgot about a dangling pointer
in the cache. Invalidate that entry when we free "base".

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Some of my changes triggered a double free fault at "free(base);" in
 t5303. This looks like a correct thing to do, but I may be missing
 something (I'm not even sure how it happened). Please check.

 sha1_file.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/sha1_file.c b/sha1_file.c
index 64228a2..99ead7c 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1912,7 +1912,8 @@ void clear_delta_base_cache(void)
 		release_delta_base_cache(&delta_base_cache[p]);
 }
 
-static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
+static struct delta_base_cache_entry *
+add_delta_base_cache(struct packed_git *p, off_t base_offset,
 	void *base, unsigned long base_size, enum object_type type)
 {
 	unsigned long hash = pack_entry_hash(p, base_offset);
@@ -1947,6 +1948,7 @@ static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
 	ent->lru.prev = delta_base_cache_lru.prev;
 	delta_base_cache_lru.prev->next = &ent->lru;
 	delta_base_cache_lru.prev = &ent->lru;
+	return ent;
 }
 
 static void *read_object(const unsigned char *sha1, enum object_type *type,
@@ -2086,12 +2088,13 @@ void *unpack_entry(struct packed_git *p, off_t obj_offset,
 		void *delta_data;
 		void *base = data;
 		unsigned long delta_size, base_size = size;
+		struct delta_base_cache_entry *ent = NULL;
 		int i;
 
 		data = NULL;
 
 		if (base)
-			add_delta_base_cache(p, obj_offset, base, base_size, type);
+			ent = add_delta_base_cache(p, obj_offset, base, base_size, type);
 
 		if (!base) {
 			/*
@@ -2129,6 +2132,8 @@ void *unpack_entry(struct packed_git *p, off_t obj_offset,
 			      "at offset %"PRIuMAX" from %s",
 			      (uintmax_t)curpos, p->pack_name);
 			free(base);
+			if (ent)
+				ent->data = NULL;
 			data = NULL;
 			continue;
 		}
-- 
1.8.2.83.gc99314b