[PATCH v2 5/5] block alloc: add validations around cache_entry lifecyle

[Jameson Miller <jamill@microsoft.com>]

Add an option (controlled by an environment variable) perform extra
validations on mem_pool allocated cache entries. When set:

  1) Invalidate cache_entry memory when discarding cache_entry.

  2) When discarding index_state struct, verify that all cache_entries
     were allocated from expected mem_pool.

  3) When discarding mem_pools, invalidate mem_pool memory.

This should provide extra checks that mem_pools and their allocated
cache_entries are being used as expected.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h      |  7 +++++++
 git.c        |  3 +++
 mem-pool.c   | 24 +++++++++++++++++++++++-
 mem-pool.h   |  2 ++
 read-cache.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/cache.h b/cache.h
index 7ed68f28e0..8f10f0649b 100644
--- a/cache.h
+++ b/cache.h
@@ -369,6 +369,13 @@ void discard_index_cache_entry(struct cache_entry *ce);
  */
 void discard_transient_cache_entry(struct cache_entry *ce);
 
+/*
+ * Validate the cache entries in the index.  This is an internal
+ * consistency check that the cache_entry structs are allocated from
+ * the expected memory pool.
+ */
+void validate_cache_entries(const struct index_state *istate);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
diff --git a/git.c b/git.c
index f598fae7b7..28ec7a6c4f 100644
--- a/git.c
+++ b/git.c
@@ -347,7 +347,10 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 
 	trace_argv_printf(argv, "trace: built-in: git");
 
+	validate_cache_entries(&the_index);
 	status = p->fn(argc, argv, prefix);
+	validate_cache_entries(&the_index);
+
 	if (status)
 		return status;
 
diff --git a/mem-pool.c b/mem-pool.c
index a495885c4b..77adb5d5b9 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -60,21 +60,43 @@ void mem_pool_discard(struct mem_pool *mem_pool)
 {
 	int i;
 	struct mp_block *block, *block_to_free;
+	int invalidate_memory = should_validate_cache_entries();
+
 	for (block = mem_pool->mp_block; block;)
 	{
 		block_to_free = block;
 		block = block->next_block;
+
+		if (invalidate_memory)
+			memset(block_to_free->space, 0xDD, ((char *)block_to_free->end) - ((char *)block_to_free->space));
+
 		free(block_to_free);
 	}
 
-	for (i = 0; i < mem_pool->nr; i++)
+	for (i = 0; i < mem_pool->nr; i++) {
+		memset(mem_pool->custom[i], 0xDD, ((char *)mem_pool->custom_end[i]) - ((char *)mem_pool->custom[i]));
 		free(mem_pool->custom[i]);
+	}
 
 	free(mem_pool->custom);
 	free(mem_pool->custom_end);
 	free(mem_pool);
 }
 
+int should_validate_cache_entries(void)
+{
+	static int validate_index_cache_entries = -1;
+
+	if (validate_index_cache_entries < 0) {
+		if (getenv("GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES"))
+			validate_index_cache_entries = 1;
+		else
+			validate_index_cache_entries = 0;
+	}
+
+	return validate_index_cache_entries;
+}
+
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
 	struct mp_block *p;
diff --git a/mem-pool.h b/mem-pool.h
index 34df4fa709..b1f9a920ba 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -63,4 +63,6 @@ void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
  */
 int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
 
+int should_validate_cache_entries(void);
+
 #endif
diff --git a/read-cache.c b/read-cache.c
index 01cd7fea41..e1dc9f7f33 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1270,6 +1270,8 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
 {
 	int pos;
 
+	validate_cache_entries(istate);
+
 	if (option & ADD_CACHE_JUST_APPEND)
 		pos = istate->cache_nr;
 	else {
@@ -1290,6 +1292,8 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
 			   istate->cache_nr - pos - 1);
 	set_index_entry(istate, pos, ce);
 	istate->cache_changed |= CE_ENTRY_ADDED;
+
+	validate_cache_entries(istate);
 	return 0;
 }
 
@@ -2013,6 +2017,8 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
+	validate_cache_entries(istate);
+
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
 	istate->cache_changed = 0;
@@ -2035,6 +2041,43 @@ int discard_index(struct index_state *istate)
 	return 0;
 }
 
+
+/*
+ * Validate the cache entries of this index.
+ * All cache entries associated with this index
+ * should have been allocated by the memory pool
+ * associated with this index, or by a referenced
+ * split index.
+ */
+void validate_cache_entries(const struct index_state *istate)
+{
+	int i;
+	int validate_index_cache_entries = should_validate_cache_entries();
+
+	if (!validate_index_cache_entries)
+		return;
+
+	if (!istate || !istate->initialized)
+		return;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		if (!istate) {
+			die("internal error: cache entry is not allocated from expected memory pool");
+		} else if (!istate->ce_mem_pool ||
+			!mem_pool_contains(istate->ce_mem_pool, istate->cache[i])) {
+			if (!istate->split_index ||
+				!istate->split_index->base ||
+				!istate->split_index->base->ce_mem_pool ||
+				!mem_pool_contains(istate->split_index->base->ce_mem_pool, istate->cache[i])) {
+				die("internal error: cache entry is not allocated from expected memory pool");
+			}
+		}
+	}
+
+	if (istate->split_index)
+		validate_cache_entries(istate->split_index->base);
+}
+
 int unmerged_index(const struct index_state *istate)
 {
 	int i;
@@ -2828,6 +2871,10 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
  */
 void discard_index_cache_entry(struct cache_entry *ce)
 {
+	int invalidate_cache_entry = should_validate_cache_entries();
+
+	if (ce && invalidate_cache_entry)
+		memset(ce, 0xCD, cache_entry_size(ce->ce_namelen));
 }
 
 void discard_transient_cache_entry(struct cache_entry *ce)
-- 
2.14.3