apply: don't segfault on binary files with missing data

Usually when applying a binary diff generated without
--binary, it will be rejected early, as we don't even have
the full sha1 of the pre- and post-images.

However, if the diff is generated with --full-index (but not
--binary), then we will actually try to apply it. If we have
the postimage blob, then we can take a shortcut and never
even look at the binary diff at all (e.g., this can happen
when rebasing changes within a repository).

If we don't have the postimage blob, though, we try to look
at the actual fragments, of which there are none, and get a
segfault. This patch checks explicitly for that case and
complains to the user instead of segfaulting. We need to
keep the check at a low level so that the "shortcut" case
above continues to work.

We also add a test that demonstrates the segfault. While
we're at it, let's also explicitly test the shortcut case.

Reported-by: Rafaël Carré <rafael.carre@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/apply.c

@@ -2645,6 +2645,12 @@ static int apply_binary_fragment(struct image *img, struct patch *patch)
 	unsigned long len;
 	void *dst;
 
+	if (!fragment)
+		return error("missing binary patch data for '%s'",
+			     patch->new_name ?
+			     patch->new_name :
+			     patch->old_name);
+
 	/* Binary patch is irreversible without the optional second hunk */
 	if (apply_in_reverse) {
 		if (!fragment->next)

t/t4103-apply-binary.sh

@@ -37,7 +37,16 @@ test_expect_success 'setup' "
 	git diff-tree -p -C master binary >C.diff &&
 
 	git diff-tree -p --binary master binary >BF.diff &&
-	git diff-tree -p --binary -C master binary >CF.diff
+	git diff-tree -p --binary -C master binary >CF.diff &&
+
+	git diff-tree -p --full-index master binary >B-index.diff &&
+	git diff-tree -p -C --full-index master binary >C-index.diff &&
+
+	git init other-repo &&
+	(cd other-repo &&
+	 git fetch .. master &&
+	 git reset --hard FETCH_HEAD
+	)
 "
 
 test_expect_success 'stat binary diff -- should not fail.' \
@@ -100,6 +109,22 @@ test_expect_success 'apply binary diff (copy) -- should fail.' \
 	'do_reset &&
 	 test_must_fail git apply --index C.diff'
 
+test_expect_success 'apply binary diff with full-index' '
+	do_reset &&
+	git apply B-index.diff
+'
+
+test_expect_success 'apply binary diff with full-index (copy)' '
+	do_reset &&
+	git apply C-index.diff
+'
+
+test_expect_success 'apply full-index binary diff in new repo' '
+	(cd other-repo &&
+	 do_reset &&
+	 test_must_fail git apply ../B-index.diff)
+'
+
 test_expect_success 'apply binary diff without replacement.' \
 	'do_reset &&
 	 git apply BF.diff'