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;

 }