When restoring a directory, allow symlinks to be followed. The full

logic here gets a little complex, but the net effect is that the
SECURE_SYMLINKS flag will prevent us from ever following a symlink.
Without it, we'll only follow symlinks to dirs.  bsdtar specifies
SECURE_SYMLINKS by default, suppresses it for -P.

I've also beefed up the write_disk_secure test to verify this
behavior.

PR:		bin/126849

2 files changed, 88 insertions, 3 deletions

diff --git a/lib/libarchive/archive_write_disk.c b/lib/libarchive/archive_write_disk.c
index b7313bc..b63a7b7 100644
--- a/lib/libarchive/archive_write_disk.c
+++ b/lib/libarchive/archive_write_disk.c
@@ -907,14 +907,26 @@ restore_entry(struct archive_write_disk *a)
 		 * We know something is in the way, but we don't know what;
 		 * we need to find out before we go any further.
 		 */
-		if (lstat(a->name, &a->st) != 0) {
+		int r = 0;
+		/*
+		 * The SECURE_SYMLINK logic has already removed a
+		 * symlink to a dir if the client wants that.  So
+		 * follow the symlink if we're creating a dir.
+		 */
+		if (S_ISDIR(a->mode))
+			r = stat(a->name, &a->st);
+		/*
+		 * If it's not a dir (or it's a broken symlink),
+		 * then don't follow it.
+		 */
+		if (r != 0 || !S_ISDIR(a->mode))
+			r = lstat(a->name, &a->st);
+		if (r != 0) {
 			archive_set_error(&a->archive, errno,
 			    "Can't stat existing object");
 			return (ARCHIVE_WARN);
 		}
 
-		/* TODO: if it's a symlink... */
-
 		/*
 		 * NO_OVERWRITE_NEWER doesn't apply to directories.
 		 */
diff --git a/lib/libarchive/test/test_write_disk_secure.c b/lib/libarchive/test/test_write_disk_secure.c
index 94e09eb..e095555 100644
--- a/lib/libarchive/test/test_write_disk_secure.c
+++ b/lib/libarchive/test/test_write_disk_secure.c
@@ -105,6 +105,79 @@ DEFINE_TEST(test_write_disk_secure)
 	archive_entry_free(ae);
 	assert(0 == archive_write_finish_entry(a));
 
+	/*
+	 * Without security checks, extracting a dir over a link to a
+	 * dir should follow the link.
+	 */
+	/* Create a symlink to a dir. */
+	assert((ae = archive_entry_new()) != NULL);
+	archive_entry_copy_pathname(ae, "link_to_dir3");
+	archive_entry_set_mode(ae, S_IFLNK | 0777);
+	archive_entry_set_symlink(ae, "dir");
+	archive_write_disk_set_options(a, 0);
+	assert(0 == archive_write_header(a, ae));
+	assert(0 == archive_write_finish_entry(a));
+	/* Extract a dir whose name matches the symlink. */
+	assert(archive_entry_clear(ae) != NULL);
+	archive_entry_copy_pathname(ae, "link_to_dir3");
+	archive_entry_set_mode(ae, S_IFDIR | 0777);
+	assert(0 == archive_write_header(a, ae));
+	assert(0 == archive_write_finish_entry(a));
+	/* Verify link was followed. */
+	assertEqualInt(0, lstat("link_to_dir3", &st));
+	assert(S_ISLNK(st.st_mode));
+	archive_entry_free(ae);
+
+	/*
+	 * As above, but a broken link, so the link should get replaced.
+	 */
+	/* Create a symlink to a dir. */
+	assert((ae = archive_entry_new()) != NULL);
+	archive_entry_copy_pathname(ae, "link_to_dir4");
+	archive_entry_set_mode(ae, S_IFLNK | 0777);
+	archive_entry_set_symlink(ae, "nonexistent_dir");
+	archive_write_disk_set_options(a, 0);
+	assert(0 == archive_write_header(a, ae));
+	assert(0 == archive_write_finish_entry(a));
+	/* Extract a dir whose name matches the symlink. */
+	assert(archive_entry_clear(ae) != NULL);
+	archive_entry_copy_pathname(ae, "link_to_dir4");
+	archive_entry_set_mode(ae, S_IFDIR | 0777);
+	assert(0 == archive_write_header(a, ae));
+	assert(0 == archive_write_finish_entry(a));
+	/* Verify link was followed. */
+	assertEqualInt(0, lstat("link_to_dir4", &st));
+	assert(S_ISDIR(st.st_mode));
+	archive_entry_free(ae);
+
+	/*
+	 * As above, but a link to a non-dir, so the link should get replaced.
+	 */
+	/* Create a regular file and a symlink to it */
+	assert((ae = archive_entry_new()) != NULL);
+	archive_entry_copy_pathname(ae, "non_dir");
+	archive_entry_set_mode(ae, S_IFREG | 0777);
+	archive_write_disk_set_options(a, 0);
+	assert(0 == archive_write_header(a, ae));
+	assert(0 == archive_write_finish_entry(a));
+	/* Create symlink to the file. */
+	archive_entry_copy_pathname(ae, "link_to_dir5");
+	archive_entry_set_mode(ae, S_IFLNK | 0777);
+	archive_entry_set_symlink(ae, "non_dir");
+	archive_write_disk_set_options(a, 0);
+	assert(0 == archive_write_header(a, ae));
+	assert(0 == archive_write_finish_entry(a));
+	/* Extract a dir whose name matches the symlink. */
+	assert(archive_entry_clear(ae) != NULL);
+	archive_entry_copy_pathname(ae, "link_to_dir5");
+	archive_entry_set_mode(ae, S_IFDIR | 0777);
+	assert(0 == archive_write_header(a, ae));
+	assert(0 == archive_write_finish_entry(a));
+	/* Verify link was followed. */
+	assertEqualInt(0, lstat("link_to_dir5", &st));
+	assert(S_ISDIR(st.st_mode));
+
+
 #if ARCHIVE_VERSION_NUMBER < 2000000
 	archive_write_finish(a);
 #else