[PATCH 1/2] help_unknown_ref(): duplicate collected refnames
- From
Jeff King <peff@peff.net>
- Date
- May 14, 2019, 12:04 UTC
- Message-ID
- <20190514120430.GA27229@sigill.intra.peff.net>
- In-Reply-To
- <20190514120220.GA7714@sigill.intra.peff.net>
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> --- help.c | 2 +- t/t7600-merge.sh | 14 ++++++++++++++ 2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/help.c b/help.c index a9e451f2ee..d3b3f64e3c 100644 --- a/help.c +++ b/help.c @@ -766,7 +766,7 @@ 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; diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh index 7f9c68cbe7..7551ae3488 100755 --- a/t/t7600-merge.sh +++ b/t/t7600-merge.sh @@ -867,4 +867,18 @@ 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
-- 2.21.0.1388.g2b1efd806f