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read-cache.c: fix writing "link" index ext with null base oid

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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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Nguyễn Thái Ngọc Duy
2019-02-13 16:51:29 +07:00
committed by Junio C Hamano
parent 98cdfbb84a
commit 6e37c8ed3c
3 changed files with 39 additions and 18 deletions
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34
split-index.c
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@ -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