mv: handle lstat() failure correctly

When moving a directory onto another with `git mv` various checks are
performed. One of of these validates that the destination is not existing.

When calling `lstat` on the destination path and it fails as the path
doesn't exist, some environments seem to overwrite the passed  in
`stat` memory nonetheless (I observed this issue on debian 12 of x86_64,
running on OrbStack on ARM, emulated with Rosetta).

This would affect the code that followed as it would still acccess a now
modified `st` structure, which now seems to contain uninitialized memory.
`S_ISDIR(st_dir_mode)` would then typically return false causing the code
to run into a bad case.

The fix avoids overwriting the existing `st` structure, providing an
alternative that exists only for that purpose.

Note that this patch minimizes complexity instead of stack-frame size.

Signed-off-by: Sebastian Thiel <sebastian.thiel@icloud.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/t/t7001-mv.sh b/t/t7001-mv.sh
index 898a920532..f136ea76f7 100755
--- a/t/t7001-mv.sh
+++ b/t/t7001-mv.sh
@@ -174,6 +174,13 @@ test_expect_success 'do not move directory over existing directory' '
 	test_must_fail git mv path2 path0
 '
 
+test_expect_success 'rename directory to non-existing directory' '
+	mkdir dir-a &&
+	>dir-a/f &&
+	git add dir-a &&
+	git mv dir-a non-existing-dir
+'
+
 test_expect_success 'move into "."' '
 	git mv path1/path2/ .
 '