Merge pull request #23206 from Luap99/rootless-reexec-userns

pkg/rootless: simplify reexec for container code

pkg/domain/infra/abi/system_linux.go

@@ -30,15 +30,16 @@ func (ic *ContainerEngine) SetupRootless(_ context.Context, noMoveProcess bool,
 		}
 	}
 
-	configureCgroup := cgroupMode != "disabled"
-	if configureCgroup {
+	hasCapSysAdmin, err := unshare.HasCapSysAdmin()
+	if err != nil {
+		return err
+	}
+
+	// check for both euid == 0 and CAP_SYS_ADMIN because we may be running in a container with CAP_SYS_ADMIN set.
+	if os.Geteuid() == 0 && hasCapSysAdmin {
 		// do it only after podman has already re-execed and running with uid==0.
-		hasCapSysAdmin, err := unshare.HasCapSysAdmin()
-		if err != nil {
-			return err
-		}
-		// check for both euid == 0 and CAP_SYS_ADMIN because we may be running in a container with CAP_SYS_ADMIN set.
-		if os.Geteuid() == 0 && hasCapSysAdmin {
+		configureCgroup := cgroupMode != "disabled"
+		if configureCgroup {
 			ownsCgroup, err := cgroups.UserOwnsCurrentSystemdCgroup()
 			if err != nil {
 				logrus.Infof("Failed to detect the owner for the current cgroup: %v", err)
@@ -55,8 +56,8 @@ func (ic *ContainerEngine) SetupRootless(_ context.Context, noMoveProcess bool,
 					}
 				}
 			}
-			return nil
 		}
+		return nil
 	}
 
 	pausePidPath, err := util.GetRootlessPauseProcessPidPath()
@@ -88,7 +89,7 @@ func (ic *ContainerEngine) SetupRootless(_ context.Context, noMoveProcess bool,
 	}
 
 	if len(paths) > 0 {
-		became, ret, err = rootless.TryJoinFromFilePaths(pausePidPath, true, paths)
+		became, ret, err = rootless.TryJoinFromFilePaths(pausePidPath, paths)
 	} else {
 		became, ret, err = rootless.BecomeRootInUserNS(pausePidPath)
 		if err == nil {

pkg/rootless/rootless.go

@@ -24,7 +24,7 @@ func TryJoinPauseProcess(pausePidPath string) (bool, int, error) {
 		return false, -1, err
 	}
 
-	became, ret, err := TryJoinFromFilePaths("", false, []string{pausePidPath})
+	became, ret, err := TryJoinFromFilePaths("", []string{pausePidPath})
 	if err == nil {
 		return became, ret, nil
 	}
@@ -45,7 +45,7 @@ func TryJoinPauseProcess(pausePidPath string) (bool, int, error) {
 	}()
 
 	// Now the pause PID file is locked.  Try to join once again in case it changed while it was not locked.
-	became, ret, err = TryJoinFromFilePaths("", false, []string{pausePidPath})
+	became, ret, err = TryJoinFromFilePaths("", []string{pausePidPath})
 	if err != nil {
 		// It is still failing.  We can safely remove it.
 		os.Remove(pausePidPath)

pkg/rootless/rootless_freebsd.go

@@ -38,11 +38,7 @@ func GetRootlessGID() int {
 // This is useful when there are already running containers and we
 // don't have a pause process yet.  We can use the paths to the conmon
 // processes to attempt joining their namespaces.
-// If needNewNamespace is set, the file is read from a temporary user
-// namespace, this is useful for containers that are running with a
-// different uidmap and the unprivileged user has no way to read the
-// file owned by the root in the container.
-func TryJoinFromFilePaths(pausePidPath string, needNewNamespace bool, paths []string) (bool, int, error) {
+func TryJoinFromFilePaths(pausePidPath string, paths []string) (bool, int, error) {
 	return false, -1, errors.New("this function is not supported on this os")
 }
 

pkg/rootless/rootless_linux.c

@@ -947,49 +947,8 @@ check_proc_sys_userns_file (const char *path)
     }
 }
 
-static int
-copy_file_to_fd (const char *file_to_read, int outfd)
-{
-  char buf[512];
-  cleanup_close int fd = -1;
-
-  fd = open (file_to_read, O_RDONLY);
-  if (fd < 0)
-    {
-      fprintf (stderr, "open `%s`: %m\n", file_to_read);
-      return fd;
-    }
-
-  for (;;)
-    {
-      ssize_t r, w, t = 0;
-
-      r = TEMP_FAILURE_RETRY (read (fd, buf, sizeof buf));
-      if (r < 0)
-        {
-          fprintf (stderr, "read from `%s`: %m\n", file_to_read);
-          return r;
-        }
-
-      if (r == 0)
-        break;
-
-      while (t < r)
-        {
-          w = TEMP_FAILURE_RETRY (write (outfd, &buf[t], r - t));
-          if (w < 0)
-            {
-              fprintf (stderr, "write file to output fd `%s`: %m\n", file_to_read);
-              return w;
-            }
-          t += w;
-        }
-    }
-  return 0;
-}
-
 int
-reexec_in_user_namespace (int ready, char *pause_pid_file_path, char *file_to_read, int outputfd)
+reexec_in_user_namespace (int ready, char *pause_pid_file_path)
 {
   cleanup_free char **argv = NULL;
   cleanup_free char *argv0 = NULL;
@@ -1138,13 +1097,6 @@ reexec_in_user_namespace (int ready, char *pause_pid_file_path, char *file_to_re
       _exit (EXIT_FAILURE);
     }
 
-  if (file_to_read && file_to_read[0])
-    {
-      ret = copy_file_to_fd (file_to_read, outputfd);
-      close (outputfd);
-      _exit (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
-    }
-
   execvp ("/proc/self/exe", argv);
   fprintf (stderr, "failed to reexec: %m\n");
 

pkg/rootless/rootless_linux.go

@@ -32,7 +32,7 @@ import (
 #include <sys/types.h>
 extern uid_t rootless_uid();
 extern uid_t rootless_gid();
-extern int reexec_in_user_namespace(int ready, char *pause_pid_file_path, char *file_to_read, int fd);
+extern int reexec_in_user_namespace(int ready, char *pause_pid_file_path);
 extern int reexec_in_user_namespace_wait(int pid, int options);
 extern int reexec_userns_join(int pid, char *pause_pid_file_path);
 extern int is_fd_inherited(int fd);
@@ -213,7 +213,7 @@ func copyMappings(from, to string) error {
 	return os.WriteFile(to, content, 0600)
 }
 
-func becomeRootInUserNS(pausePid, fileToRead string, fileOutput *os.File) (_ bool, _ int, retErr error) {
+func becomeRootInUserNS(pausePid string) (_ bool, _ int, retErr error) {
 	hasCapSysAdmin, err := unshare.HasCapSysAdmin()
 	if err != nil {
 		return false, 0, err
@@ -249,13 +249,6 @@ func becomeRootInUserNS(pausePid, fileToRead string, fileOutput *os.File) (_ boo
 	cPausePid := C.CString(pausePid)
 	defer C.free(unsafe.Pointer(cPausePid))
 
-	cFileToRead := C.CString(fileToRead)
-	defer C.free(unsafe.Pointer(cFileToRead))
-	var fileOutputFD C.int
-	if fileOutput != nil {
-		fileOutputFD = C.int(fileOutput.Fd())
-	}
-
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
 
@@ -287,7 +280,7 @@ func becomeRootInUserNS(pausePid, fileToRead string, fileOutput *os.File) (_ boo
 		}
 	}()
 
-	pidC := C.reexec_in_user_namespace(C.int(r.Fd()), cPausePid, cFileToRead, fileOutputFD)
+	pidC := C.reexec_in_user_namespace(C.int(r.Fd()), cPausePid)
 	pid = int(pidC)
 	if pid < 0 {
 		return false, -1, fmt.Errorf("cannot re-exec process")
@@ -361,14 +354,6 @@ func becomeRootInUserNS(pausePid, fileToRead string, fileOutput *os.File) (_ boo
 		return false, -1, fmt.Errorf("read from sync pipe: %w", err)
 	}
 
-	if fileOutput != nil {
-		ret := C.reexec_in_user_namespace_wait(pidC, 0)
-		if ret < 0 {
-			return false, -1, errors.New("waiting for the re-exec process")
-		}
-		return true, 0, nil
-	}
-
 	if b[0] == '2' {
 		// We have lost the race for writing the PID file, as probably another
 		// process created a namespace and wrote the PID.
@@ -434,69 +419,27 @@ func waitAndProxySignalsToChild(pid C.int) (bool, int, error) {
 // If podman was re-executed the caller needs to propagate the error code returned by the child
 // process.
 func BecomeRootInUserNS(pausePid string) (bool, int, error) {
-	return becomeRootInUserNS(pausePid, "", nil)
+	return becomeRootInUserNS(pausePid)
 }
 
 // TryJoinFromFilePaths attempts to join the namespaces of the pid files in paths.
 // This is useful when there are already running containers and we
 // don't have a pause process yet.  We can use the paths to the conmon
 // processes to attempt joining their namespaces.
-// If needNewNamespace is set, the file is read from a temporary user
-// namespace, this is useful for containers that are running with a
-// different uidmap and the unprivileged user has no way to read the
-// file owned by the root in the container.
-func TryJoinFromFilePaths(pausePidPath string, needNewNamespace bool, paths []string) (bool, int, error) {
+func TryJoinFromFilePaths(pausePidPath string, paths []string) (bool, int, error) {
 	var lastErr error
-	var pausePid int
 
 	for _, path := range paths {
-		if !needNewNamespace {
-			data, err := os.ReadFile(path)
-			if err != nil {
-				lastErr = err
-				continue
-			}
-
-			pausePid, err = strconv.Atoi(string(data))
-			if err != nil {
-				lastErr = fmt.Errorf("cannot parse file %q: %w", path, err)
-				continue
-			}
-		} else {
-			r, w, err := os.Pipe()
-			if err != nil {
-				lastErr = err
-				continue
-			}
-
-			defer errorhandling.CloseQuiet(r)
-
-			if _, _, err := becomeRootInUserNS("", path, w); err != nil {
-				w.Close()
-				lastErr = err
-				continue
-			}
-
-			if err := w.Close(); err != nil {
-				return false, 0, err
-			}
-			defer func() {
-				C.reexec_in_user_namespace_wait(-1, 0)
-			}()
-
-			b := make([]byte, 32)
-
-			n, err := r.Read(b)
-			if err != nil {
-				lastErr = fmt.Errorf("cannot read %q: %w", path, err)
-				continue
-			}
+		data, err := os.ReadFile(path)
+		if err != nil {
+			lastErr = err
+			continue
+		}
 
-			pausePid, err = strconv.Atoi(string(b[:n]))
-			if err != nil {
-				lastErr = err
-				continue
-			}
+		pausePid, err := strconv.Atoi(string(data))
+		if err != nil {
+			lastErr = fmt.Errorf("cannot parse file %q: %w", path, err)
+			continue
 		}
 
 		if pausePid > 0 && unix.Kill(pausePid, 0) == nil {

pkg/rootless/rootless_unsupported.go

@@ -41,11 +41,7 @@ func GetRootlessGID() int {
 // This is useful when there are already running containers and we
 // don't have a pause process yet.  We can use the paths to the conmon
 // processes to attempt joining their namespaces.
-// If needNewNamespace is set, the file is read from a temporary user
-// namespace, this is useful for containers that are running with a
-// different uidmap and the unprivileged user has no way to read the
-// file owned by the root in the container.
-func TryJoinFromFilePaths(pausePidPath string, needNewNamespace bool, paths []string) (bool, int, error) {
+func TryJoinFromFilePaths(pausePidPath string, paths []string) (bool, int, error) {
 	return false, -1, errors.New("this function is not supported on this os")
 }
 

test/system/550-pause-process.bats

@@ -119,7 +119,7 @@ function _check_pause_process() {
 
     # First let's run a container in the background to keep the userns active
     local cname1=c1_$(random_string)
-    run_podman run -d --name $cname1 $IMAGE top
+    run_podman run -d --name $cname1 --uidmap 0:100:100 $IMAGE top
 
     run_podman unshare readlink /proc/self/ns/user
     userns="$output"
@@ -136,6 +136,9 @@ function _check_pause_process() {
 
     _test_sigproxy $cname2 $kidpid
 
+    # check pause process again
+    _check_pause_process
+
     # our container exits 0 so podman should too
     wait $kidpid || die "podman run exited $? instead of zero"