[PATCH 1/6] hash-object: fix buffer reuse with --path in a subdirectory

[Jeff King <peff@peff.net>]

The hash-object command uses prefix_filename() without
duplicating its return value. Since that function returns a
static buffer, the value is overwritten by subsequent calls.

This can cause incorrect results when we use --path along
with hashing a file by its relative path, both of which need
to call prefix_filename(). We overwrite the filename
computed for --path, effectively ignoring it.

We can fix this by calling xstrdup on the return value. Note
that we don't bother freeing the "vpath" instance, as it
remains valid until the program exit.

Signed-off-by: Jeff King <peff@peff.net>
---
 builtin/hash-object.c  |  7 +++++--
 t/t1007-hash-object.sh | 10 ++++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/builtin/hash-object.c b/builtin/hash-object.c
index 9028e1fdc..56df77b0c 100644
--- a/builtin/hash-object.c
+++ b/builtin/hash-object.c
@@ -115,7 +115,7 @@ int cmd_hash_object(int argc, const char **argv, const char *prefix)
 
 	prefix_length = prefix ? strlen(prefix) : 0;
 	if (vpath && prefix)
-		vpath = prefix_filename(prefix, prefix_length, vpath);
+		vpath = xstrdup(prefix_filename(prefix, prefix_length, vpath));
 
 	git_config(git_default_config, NULL);
 
@@ -144,11 +144,14 @@ int cmd_hash_object(int argc, const char **argv, const char *prefix)
 
 	for (i = 0 ; i < argc; i++) {
 		const char *arg = argv[i];
+		char *to_free = NULL;
 
 		if (0 <= prefix_length)
-			arg = prefix_filename(prefix, prefix_length, arg);
+			arg = to_free =
+				xstrdup(prefix_filename(prefix, prefix_length, arg));
 		hash_object(arg, type, no_filters ? NULL : vpath ? vpath : arg,
 			    flags, literally);
+		free(to_free);
 	}
 
 	if (stdin_paths)
diff --git a/t/t1007-hash-object.sh b/t/t1007-hash-object.sh
index c5245c5cb..532682f51 100755
--- a/t/t1007-hash-object.sh
+++ b/t/t1007-hash-object.sh
@@ -134,6 +134,16 @@ test_expect_success 'gitattributes also work in a subdirectory' '
 	)
 '
 
+test_expect_success '--path works in a subdirectory' '
+	(
+		cd subdir &&
+		path1_sha=$(git hash-object --path=../file1 ../file0) &&
+		path0_sha=$(git hash-object --path=../file0 ../file1) &&
+		test "$file0_sha" = "$path0_sha" &&
+		test "$file1_sha" = "$path1_sha"
+	)
+'
+
 test_expect_success 'check that --no-filters option works' '
 	nofilters_file1=$(git hash-object --no-filters file1) &&
 	test "$file0_sha" = "$nofilters_file1" &&
-- 
2.12.1.683.gcd02edfec