From: Mike Yuan <me@yhndnzj.com>
Date: Sun, 1 Jun 2025 06:55:50 +0000 (+0200)
Subject: pidfd-util: open an internal pidfd if none is passed in pidfd_check_pidfs()
X-Git-Tag: v258-rc1~390^2~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e09b7ced6557135becc8f5fb6dc23db753772124;p=thirdparty%2Fsystemd.git

pidfd-util: open an internal pidfd if none is passed in pidfd_check_pidfs()

I'd like to introduce a libsystemd helper for acquiring pidfd
inode id, which however means the fd passed to pidfd_check_pidfs()
can no longer be trusted. Let's add back the logic of allocating
a genuine pidfd allocated internally, which was remove in
5dc9d5b4eacbe32f58ad6ca18d70931ab89ea409.
---

diff --git a/src/basic/pidfd-util.c b/src/basic/pidfd-util.c
index f53a94f2d3e..629ffe95961 100644
--- a/src/basic/pidfd-util.c
+++ b/src/basic/pidfd-util.c
@@ -26,6 +26,15 @@ static int pidfd_check_pidfs(int pid_fd) {
         if (have_pidfs >= 0)
                 return have_pidfs;
 
+        _cleanup_close_ int our_fd = -EBADF;
+        if (pid_fd < 0) {
+                our_fd = pidfd_open(getpid_cached(), /* flags = */ 0);
+                if (our_fd < 0)
+                        return -errno;
+
+                pid_fd = our_fd;
+        }
+
         return (have_pidfs = fd_is_fs_type(pid_fd, PID_FS_MAGIC));
 }