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help_unknown_ref(): duplicate collected refnames 

When "git merge" sees an unknown refname, we iterate through the refs to
try to suggest some possible alternates. We do so with for_each_ref(),
and in the callback we add some of the refnames we get to a
string_list that is declared with NODUP, directly adding a pointer into
the refname string our callback received.

But the for_each_ref() machinery does not promise that the refname
string will remain valid, and as a result we may print garbage memory.

The code in question dates back to its inception in e56181060e (help:
add help_unknown_ref(), 2013-05-04). But back then, the refname strings
generally did remain stable, at least immediately after the
for_each_ref() call. Later, in d1cf15516f (packed_ref_iterator_begin():
iterate using `mmapped_ref_iterator`, 2017-09-25), we started
consistently re-using a separate buffer for packed refs.

The fix is simple: duplicate the strings we intend to collect. We
already call string_list_clear(), so the memory is correctly freed.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2019-05-14 08:04:31 -04:00 committed by Junio C Hamano
parent aeb582a983
commit 8ed51b0666
2 changed files with 15 additions and 1 deletions
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2
help.c
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@ -773,7 +773,7 @@ static int append_similar_ref(const char *refname, const struct object_id *oid,
static struct string_list guess_refs(const char *ref)
{
struct similar_ref_cb ref_cb;
struct string_list similar_refs = STRING_LIST_INIT_NODUP;
struct string_list similar_refs = STRING_LIST_INIT_DUP;
ref_cb.base_ref = ref;
ref_cb.similar_refs = &similar_refs;

14
t/t7600-merge.sh
View File

@ -822,4 +822,18 @@ test_expect_success EXECKEEPSPID 'killed merge can be completed with --continue'
verify_parents $c0 $c1
'
test_expect_success 'merge suggests matching remote refname' '
git commit --allow-empty -m not-local &&
git update-ref refs/remotes/origin/not-local HEAD &&
git reset --hard HEAD^ &&
# This is white-box testing hackery; we happen to know
# that reading packed refs is more picky about the memory
# ownership of strings we pass to for_each_ref() callbacks.
git pack-refs --all --prune &&
test_must_fail git merge not-local 2>stderr &&
grep origin/not-local stderr
'
test_done