From 6cb356ca9fe063846cfb883ef484f7e7e411096c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Tue, 3 Mar 2020 11:51:50 +0100
Subject: [PATCH 2/3] basic/fs-util: add a version of chmod_and_chown that
 doesn not use  /proc

---
 src/basic/fs-util.c     | 46 +++++++++++++++++++++++++++++++++++++++++
 src/basic/fs-util.h     |  1 +
 src/test/test-fs-util.c | 45 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 92 insertions(+)

diff --git a/src/basic/fs-util.c b/src/basic/fs-util.c
index f8095e85d8..558cafbcaf 100644
--- a/src/basic/fs-util.c
+++ b/src/basic/fs-util.c
@@ -272,6 +272,52 @@ int fchmod_and_chown(int fd, mode_t mode, uid_t uid, gid_t gid) {
         return do_chown || do_chmod;
 }
 
+int chmod_and_chown_unsafe(const char *path, mode_t mode, uid_t uid, gid_t gid) {
+        bool do_chown, do_chmod;
+        struct stat st;
+
+        assert(path);
+
+        /* Change ownership and access mode of the specified path, see description of fchmod_and_chown().
+         * Should only be used on trusted paths. */
+
+        if (lstat(path, &st) < 0)
+                return -errno;
+
+        do_chown =
+                (uid != UID_INVALID && st.st_uid != uid) ||
+                (gid != GID_INVALID && st.st_gid != gid);
+
+        do_chmod =
+                !S_ISLNK(st.st_mode) && /* chmod is not defined on symlinks */
+                ((mode != MODE_INVALID && ((st.st_mode ^ mode) & 07777) != 0) ||
+                 do_chown); /* If we change ownership, make sure we reset the mode afterwards, since chown()
+                             * modifies the access mode too */
+
+        if (mode == MODE_INVALID)
+                mode = st.st_mode; /* If we only shall do a chown(), save original mode, since chown() might break it. */
+        else if ((mode & S_IFMT) != 0 && ((mode ^ st.st_mode) & S_IFMT) != 0)
+                return -EINVAL; /* insist on the right file type if it was specified */
+
+        if (do_chown && do_chmod) {
+                mode_t minimal = st.st_mode & mode; /* the subset of the old and the new mask */
+
+                if (((minimal ^ st.st_mode) & 07777) != 0)
+                        if (chmod(path, minimal & 07777) < 0)
+                                return -errno;
+        }
+
+        if (do_chown)
+                if (lchown(path, uid, gid) < 0)
+                        return -errno;
+
+        if (do_chmod)
+                if (chmod(path, mode & 07777) < 0)
+                        return -errno;
+
+        return do_chown || do_chmod;
+}
+
 int fchmod_umask(int fd, mode_t m) {
         mode_t u;
         int r;
diff --git a/src/basic/fs-util.h b/src/basic/fs-util.h
index 78d68be9fd..6b9ade2ec1 100644
--- a/src/basic/fs-util.h
+++ b/src/basic/fs-util.h
@@ -34,6 +34,7 @@ int readlink_and_make_absolute(const char *p, char **r);
 
 int chmod_and_chown(const char *path, mode_t mode, uid_t uid, gid_t gid);
 int fchmod_and_chown(int fd, mode_t mode, uid_t uid, gid_t gid);
+int chmod_and_chown_unsafe(const char *path, mode_t mode, uid_t uid, gid_t gid);
 
 int fchmod_umask(int fd, mode_t mode);
 int fchmod_opath(int fd, mode_t m);
diff --git a/src/test/test-fs-util.c b/src/test/test-fs-util.c
index d0c6fb82bf..d97ccfda3b 100644
--- a/src/test/test-fs-util.c
+++ b/src/test/test-fs-util.c
@@ -802,6 +802,50 @@ static void test_chmod_and_chown(void) {
         assert_se(S_ISLNK(st.st_mode));
 }
 
+static void test_chmod_and_chown_unsafe(void) {
+        _cleanup_(rm_rf_physical_and_freep) char *d = NULL;
+        _unused_ _cleanup_umask_ mode_t u = umask(0000);
+        struct stat st;
+        const char *p;
+
+        if (geteuid() != 0)
+                return;
+
+        log_info("/* %s */", __func__);
+
+        assert_se(mkdtemp_malloc(NULL, &d) >= 0);
+
+        p = strjoina(d, "/reg");
+        assert_se(mknod(p, S_IFREG | 0123, 0) >= 0);
+
+        assert_se(chmod_and_chown_unsafe(p, S_IFREG | 0321, 1, 2) >= 0);
+        assert_se(chmod_and_chown_unsafe(p, S_IFDIR | 0555, 3, 4) == -EINVAL);
+
+        assert_se(lstat(p, &st) >= 0);
+        assert_se(S_ISREG(st.st_mode));
+        assert_se((st.st_mode & 07777) == 0321);
+
+        p = strjoina(d, "/dir");
+        assert_se(mkdir(p, 0123) >= 0);
+
+        assert_se(chmod_and_chown_unsafe(p, S_IFDIR | 0321, 1, 2) >= 0);
+        assert_se(chmod_and_chown_unsafe(p, S_IFREG | 0555, 3, 4) == -EINVAL);
+
+        assert_se(lstat(p, &st) >= 0);
+        assert_se(S_ISDIR(st.st_mode));
+        assert_se((st.st_mode & 07777) == 0321);
+
+        p = strjoina(d, "/lnk");
+        assert_se(symlink("idontexist", p) >= 0);
+
+        assert_se(chmod_and_chown_unsafe(p, S_IFLNK | 0321, 1, 2) >= 0);
+        assert_se(chmod_and_chown_unsafe(p, S_IFREG | 0555, 3, 4) == -EINVAL);
+        assert_se(chmod_and_chown_unsafe(p, S_IFDIR | 0555, 3, 4) == -EINVAL);
+
+        assert_se(lstat(p, &st) >= 0);
+        assert_se(S_ISLNK(st.st_mode));
+}
+
 int main(int argc, char *argv[]) {
         test_setup_logging(LOG_INFO);
 
@@ -819,6 +863,7 @@ int main(int argc, char *argv[]) {
         test_fsync_directory_of_file();
         test_rename_noreplace();
         test_chmod_and_chown();
+        test_chmod_and_chown_unsafe();
 
         return 0;
 }