[PATCH v4 3/4] apply: do not read from beyond a symbolic link

[Junio C Hamano <gitster@pobox.com>]

We should reject a patch, whether it renames/copies dir/file to
elsewhere with or without modificiation, or updates dir/file in
place, if "dir/" part is actually a symbolic link to elsewhere,
by making sure that the code to read the preimage does not read
from a path that is beyond a symbolic link.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/apply.c                 |  2 ++
 t/t4122-apply-symlink-inside.sh | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/builtin/apply.c b/builtin/apply.c
index 21e45a0..422e4ce 100644
--- a/builtin/apply.c
+++ b/builtin/apply.c
@@ -3145,6 +3145,8 @@ static int load_patch_target(struct strbuf *buf,
 				return read_file_or_gitlink(ce, buf);
 			else
 				return SUBMODULE_PATCH_WITHOUT_INDEX;
+		} else if (has_symlink_leading_path(name, strlen(name))) {
+			return error(_("reading from '%s' beyond a symbolic link"), name);
 		} else {
 			if (read_old_data(st, name, buf))
 				return error(_("read of %s failed"), name);
diff --git a/t/t4122-apply-symlink-inside.sh b/t/t4122-apply-symlink-inside.sh
index 70b3a06..035c080 100755
--- a/t/t4122-apply-symlink-inside.sh
+++ b/t/t4122-apply-symlink-inside.sh
@@ -52,4 +52,23 @@ test_expect_success 'check result' '
 
 '
 
+test_expect_success SYMLINKS 'do not read from beyond symbolic link' '
+	git reset --hard &&
+	mkdir -p arch/x86_64/dir &&
+	>arch/x86_64/dir/file &&
+	git add arch/x86_64/dir/file &&
+	echo line >arch/x86_64/dir/file &&
+	git diff >patch &&
+	git reset --hard &&
+
+	mkdir arch/i386/dir &&
+	>arch/i386/dir/file &&
+	ln -s ../i386/dir arch/x86_64/dir &&
+
+	test_must_fail git apply patch &&
+	test_must_fail git apply --cached patch &&
+	test_must_fail git apply --index patch
+
+'
+
 test_done
-- 
2.3.0-185-g073f588