repo: NUL terminate readlinkat result

Makefile-tests.am

@@ -73,6 +73,7 @@ _installed_or_uninstalled_test_scripts = \
 	tests/test-remote-headers.sh \
 	tests/test-remote-refs.sh \
 	tests/test-composefs.sh \
+	tests/test-payload-link.sh \
 	tests/test-commit-sign.sh \
 	tests/test-commit-timestamp.sh \
 	tests/test-export.sh \

src/libostree/ostree-repo-commit.c

@@ -794,7 +794,7 @@ _try_clone_from_payload_link (OstreeRepo *self, OstreeRepo *dest_repo, const cha
       glnx_autofd int fdf = -1;
       char loose_path_buf[_OSTREE_LOOSE_PATH_MAX];
       char loose_path_target_buf[_OSTREE_LOOSE_PATH_MAX];
-      char target_buf[_OSTREE_LOOSE_PATH_MAX + _OSTREE_PAYLOAD_LINK_PREFIX_LEN];
+      char target_buf[_OSTREE_LOOSE_PATH_MAX + _OSTREE_PAYLOAD_LINK_PREFIX_LEN + 1];
       char target_checksum[OSTREE_SHA256_STRING_LEN + 1];
       int dfd = dfd_searches[i];
       ssize_t size;
@@ -804,16 +804,21 @@ _try_clone_from_payload_link (OstreeRepo *self, OstreeRepo *dest_repo, const cha
       _ostree_loose_path (loose_path_buf, payload_checksum, OSTREE_OBJECT_TYPE_PAYLOAD_LINK,
                           self->mode);
 
-      size = TEMP_FAILURE_RETRY (readlinkat (dfd, loose_path_buf, target_buf, sizeof (target_buf)));
+      size = TEMP_FAILURE_RETRY (
+          readlinkat (dfd, loose_path_buf, target_buf, sizeof (target_buf) - 1));
       if (size < 0)
         {
           if (errno == ENOENT)
             continue;
           return glnx_throw_errno_prefix (error, "readlinkat");
         }
+      target_buf[size] = '\0';
 
+      const size_t expected_len = OSTREE_SHA256_STRING_LEN + _OSTREE_PAYLOAD_LINK_PREFIX_LEN;
       if (size < OSTREE_SHA256_STRING_LEN + _OSTREE_PAYLOAD_LINK_PREFIX_LEN)
-        return glnx_throw (error, "invalid data size for %s", loose_path_buf);
+        return glnx_throw (error, "invalid data size for %s; expected=%llu found=%llu",
+                           loose_path_buf, (unsigned long long)expected_len,
+                           (unsigned long long)size);
 
       snprintf (target_checksum, size, "%.2s%.62s", target_buf + _OSTREE_PAYLOAD_LINK_PREFIX_LEN,
                 target_buf + _OSTREE_PAYLOAD_LINK_PREFIX_LEN + 3);

tests/test-payload-link.sh

@@ -0,0 +1,46 @@
+#!/bin/bash
+#
+# Copyright (C) 2024 Red Hat, Inc.
+#
+# SPDX-License-Identifier: LGPL-2.0+
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library. If not, see <https://www.gnu.org/licenses/>.
+
+set -euox pipefail
+
+. $(dirname $0)/libtest.sh
+
+touch foo
+if ! cp --reflink=always foo bar &>/dev/null; then
+    skip "no reflinks"
+fi
+rm foo bar
+
+$CMD_PREFIX ostree --repo=repo init --mode=bare-user
+$CMD_PREFIX ostree config --repo=repo set core.payload-link-threshold 0
+
+mkdir d
+echo test > d/testcontent
+chmod 0644 d/testcontent
+$CMD_PREFIX ostree --repo=repo commit --tree=dir=d --consume -b testref
+mkdir d
+echo test > d/testcontent
+chmod 0755 d/testcontent
+$CMD_PREFIX ostree --repo=repo commit --tree=dir=d --consume -b testref
+find repo -type l -name '*.payload-link' >payload-links.txt
+assert_streq "$(wc -l < payload-links.txt)" "1"
+
+tap_ok payload-link
+
+tap_end