1 files changed, 37 insertions, 0 deletions
diff --git a/src/systemd/src/basic/fd-util.c b/src/systemd/src/basic/fd-util.c
index 82944908e8..971f5ec5e8 100644
--- a/src/systemd/src/basic/fd-util.c
+++ b/src/systemd/src/basic/fd-util.c
@@ -584,3 +584,40 @@ try_dev_shm_without_o_tmpfile:
         return -EOPNOTSUPP;
 }
 #endif /* NM_IGNORED */
+
+int fd_move_above_stdio(int fd) {
+        int flags, copy;
+        PROTECT_ERRNO;
+
+        /* Moves the specified file descriptor if possible out of the range [0…2], i.e. the range of
+         * stdin/stdout/stderr. If it can't be moved outside of this range the original file descriptor is
+         * returned. This call is supposed to be used for long-lasting file descriptors we allocate in our code that
+         * might get loaded into foreign code, and where we want ensure our fds are unlikely used accidentally as
+         * stdin/stdout/stderr of unrelated code.
+         *
+         * Note that this doesn't fix any real bugs, it just makes it less likely that our code will be affected by
+         * buggy code from others that mindlessly invokes 'fprintf(stderr, …' or similar in places where stderr has
+         * been closed before.
+         *
+         * This function is written in a "best-effort" and "least-impact" style. This means whenever we encounter an
+         * error we simply return the original file descriptor, and we do not touch errno. */
+
+        if (fd < 0 || fd > 2)
+                return fd;
+
+        flags = fcntl(fd, F_GETFD, 0);
+        if (flags < 0)
+                return fd;
+
+        if (flags & FD_CLOEXEC)
+                copy = fcntl(fd, F_DUPFD_CLOEXEC, 3);
+        else
+                copy = fcntl(fd, F_DUPFD, 3);
+        if (copy < 0)
+                return fd;
+
+        assert(copy > 2);
+
+        (void) close(fd);
+        return copy;
+}