[PATCH v2] read-cache.c: fix writing "link" index ext with null base oid
Since commit 7db118303a (unpack_trees: fix breakage when o->src_index != o->dst_index - 2018-04-23) and changes in merge code to use separate index_state for source and destination, when doing a merge with split index activated, we may run into this line in unpack_trees():
o->result.split_index = init_split_index(&o->result);
This is by itself not wrong. But this split index information is not fully populated (and it's only so when move_cache_to_base_index() is called, aka force splitting the index, or loading index_state from a file). Both "base_oid" and "base" in this case remain null.
So when writing the main index down, we link to this index with null oid (default value after init_split_index()), which also means "no split index" internally. This triggers an incorrect base index refresh:
warning: could not freshen shared index '.../sharedindex.0{40}'This patch makes sure we will not refresh null base_oid (because the file is never there). It also makes sure not to write "link" extension with null base_oid in the first place (no point having it at all). Read code already has protection against null base_oid.
There is also another side fix in remove_split_index() that causes a crash when doing "git update-index --no-split-index" when base_oid in the index file is null. In this case we will not load istate->split_index->base but we dereference it anyway and are rewarded with a segfault. This should not happen anymore, but it's still wrong to dereference a potential NULL pointer, especially when we do check for NULL pointer in the next code.
Reported-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
v2 added a new test
read-cache.c | 5 +++--
split-index.c | 34 ++++++++++++++++++----------------
t/t1700-split-index.sh | 18 ++++++++++++++++++
3 files changed, 39 insertions(+), 18 deletions(-)
diff --git a/read-cache.c b/read-cache.c
index 8f644f68b4..d140b44f8f 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2520,7 +2520,8 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
return err;
/* Write extension data here */
- if (!strip_extensions && istate->split_index) {
+ if (!strip_extensions && istate->split_index &&
+ !is_null_oid(&istate->split_index->base_oid)) {
struct strbuf sb = STRBUF_INIT;
err = write_link_extension(&sb, istate) < 0 ||
@@ -2794,7 +2795,7 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
ret = write_split_index(istate, lock, flags);
/* Freshen the shared index only if the split-index was written */
- if (!ret && !new_shared_index) {
+ if (!ret && !new_shared_index && !is_null_oid(&si->base_oid)) {
const char *shared_index = git_path("sharedindex.%s",
oid_to_hex(&si->base_oid));
freshen_shared_index(shared_index, 1);
diff --git a/split-index.c b/split-index.c
index 5820412dc5..a9d13611a4 100644
--- a/split-index.c
+++ b/split-index.c
@@ -440,24 +440,26 @@ void add_split_index(struct index_state *istate)
void remove_split_index(struct index_state *istate)
{
if (istate->split_index) {
- /*
- * When removing the split index, we need to move
- * ownership of the mem_pool associated with the
- * base index to the main index. There may be cache entries
- * allocated from the base's memory pool that are shared with
- * the_index.cache[].
- */
- mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+ if (istate->split_index->base) {
+ /*
+ * When removing the split index, we need to move
+ * ownership of the mem_pool associated with the
+ * base index to the main index. There may be cache entries
+ * allocated from the base's memory pool that are shared with
+ * the_index.cache[].
+ */
+ mem_pool_combine(istate->ce_mem_pool,
+ istate->split_index->base->ce_mem_pool);
- /*
- * The split index no longer owns the mem_pool backing
- * its cache array. As we are discarding this index,
- * mark the index as having no cache entries, so it
- * will not attempt to clean up the cache entries or
- * validate them.
- */
- if (istate->split_index->base)
+ /*
+ * The split index no longer owns the mem_pool backing
+ * its cache array. As we are discarding this index,
+ * mark the index as having no cache entries, so it
+ * will not attempt to clean up the cache entries or
+ * validate them.
+ */
istate->split_index->base->cache_nr = 0;
+ }
/*
* We can discard the split index because its
diff --git a/t/t1700-split-index.sh b/t/t1700-split-index.sh
index f053bf83eb..ea5181aff9 100755
--- a/t/t1700-split-index.sh
+++ b/t/t1700-split-index.sh
@@ -447,4 +447,22 @@ test_expect_success 'writing split index with null sha1 does not write cache tre
test_line_count = 0 cache-tree.out
'
+test_expect_success 'do not refresh null base index' '
+ test_create_repo merge &&
+ (
+ cd merge &&
+ test_commit initial &&
+ git checkout -b side-branch &&
+ test_commit extra &&
+ git checkout master &&
+ git update-index --split-index &&
+ test_commit more &&
+ # must not write a new shareindex, or we wont catch the problem
+ git -c splitIndex.maxPercentChange=100 merge --no-edit side-branch 2>err &&
+ # i.e. do not expect warnings like
+ # could not freshen shared index .../shareindex.00000...
+ test_must_be_empty err
+ )
+'
+
test_done
--
2.21.0.rc0.328.g0e39304f8d
Luke Diamand
