cri: Make sure host sandbox files exist before adding them to mounts

As `setupSandboxFiles` was done in sandbox controller, it is difficult
here to know if the sandbox controller has done and where the host path
in. Make sure the host path exists before adding them to linux container
mounts, otherwise, the container would generate some unnecessary mounts.

Signed-off-by: Zhang Tianyang <burning9699@gmail.com>

Author: Burning1020

internal/cri/server/container_create.go

@@ -1008,51 +1008,65 @@ func (c *criService) linuxContainerMounts(sandboxID string, config *runtime.Cont
 	}
 
 	if !isInCRIMounts(etcHosts, config.GetMounts()) {
-		mounts = append(mounts, &runtime.Mount{
-			ContainerPath:  etcHosts,
-			HostPath:       c.getSandboxHosts(sandboxID),
-			Readonly:       securityContext.GetReadonlyRootfs(),
-			SelinuxRelabel: true,
-			UidMappings:    uidMappings,
-			GidMappings:    gidMappings,
-		})
+		hostpath := c.getSandboxHosts(sandboxID)
+		// /etc/hosts could be delegated to remote sandbox controller. That file isn't required to be existed
+		// in host side for some sandbox runtimes. Skip it if we don't need it.
+		if _, err := c.os.Stat(hostpath); err == nil {
+			mounts = append(mounts, &runtime.Mount{
+				ContainerPath:  etcHosts,
+				HostPath:       hostpath,
+				Readonly:       securityContext.GetReadonlyRootfs(),
+				SelinuxRelabel: true,
+				UidMappings:    uidMappings,
+				GidMappings:    gidMappings,
+			})
+		}
 	}
 
 	// Mount sandbox resolv.config.
 	// TODO: Need to figure out whether we should always mount it as read-only
 	if !isInCRIMounts(resolvConfPath, config.GetMounts()) {
-		mounts = append(mounts, &runtime.Mount{
-			ContainerPath:  resolvConfPath,
-			HostPath:       c.getResolvPath(sandboxID),
-			Readonly:       securityContext.GetReadonlyRootfs(),
-			SelinuxRelabel: true,
-			UidMappings:    uidMappings,
-			GidMappings:    gidMappings,
-		})
+		hostpath := c.getResolvPath(sandboxID)
+		// The ownership of /etc/resolv.conf could be delegated to remote sandbox controller. That file isn't
+		// required to be existed in host side for some sandbox runtimes. Skip it if we don't need it.
+		if _, err := c.os.Stat(hostpath); err == nil {
+			mounts = append(mounts, &runtime.Mount{
+				ContainerPath:  resolvConfPath,
+				HostPath:       hostpath,
+				Readonly:       securityContext.GetReadonlyRootfs(),
+				SelinuxRelabel: true,
+				UidMappings:    uidMappings,
+				GidMappings:    gidMappings,
+			})
+		}
 	}
 
 	if !isInCRIMounts(devShm, config.GetMounts()) {
 		sandboxDevShm := c.getSandboxDevShm(sandboxID)
 		if securityContext.GetNamespaceOptions().GetIpc() == runtime.NamespaceMode_NODE {
 			sandboxDevShm = devShm
 		}
-		mounts = append(mounts, &runtime.Mount{
-			ContainerPath:  devShm,
-			HostPath:       sandboxDevShm,
-			Readonly:       false,
-			SelinuxRelabel: sandboxDevShm != devShm,
-			// XXX: tmpfs support for idmap mounts got merged in
-			// Linux 6.3.
-			// Our Ubuntu 22.04 CI runs with 5.15 kernels, so
-			// disabling idmap mounts for this case makes the CI
-			// happy (the other fs used support idmap mounts in 5.15
-			// kernels).
-			// We can enable this at a later stage, but as this
-			// tmpfs mount is exposed empty to the container (no
-			// prepopulated files) and using the hostIPC with userns
-			// is blocked by k8s, we can just avoid using the
-			// mappings and it should work fine.
-		})
+		// The ownership of /dev/shm could be delegated to remote sandbox controller. That file isn't required
+		// to be existed in host side for some sandbox runtimes. Skip it if we don't need it.
+		if _, err := c.os.Stat(sandboxDevShm); err == nil {
+			mounts = append(mounts, &runtime.Mount{
+				ContainerPath:  devShm,
+				HostPath:       sandboxDevShm,
+				Readonly:       false,
+				SelinuxRelabel: sandboxDevShm != devShm,
+				// XXX: tmpfs support for idmap mounts got merged in
+				// Linux 6.3.
+				// Our Ubuntu 22.04 CI runs with 5.15 kernels, so
+				// disabling idmap mounts for this case makes the CI
+				// happy (the other fs used support idmap mounts in 5.15
+				// kernels).
+				// We can enable this at a later stage, but as this
+				// tmpfs mount is exposed empty to the container (no
+				// prepopulated files) and using the hostIPC with userns
+				// is blocked by k8s, we can just avoid using the
+				// mappings and it should work fine.
+			})
+		}
 	}
 	return mounts
 }

internal/cri/server/container_create_test.go

@@ -733,32 +733,21 @@ func TestLinuxContainerMounts(t *testing.T) {
 			expectedMounts:  nil,
 		},
 		{
-			desc: "should skip hostname mount if the old sandbox doesn't have hostname file",
+			desc: "should skip sandbox mounts if the old sandbox doesn't have sandbox file",
 			statFn: func(path string) (os.FileInfo, error) {
-				assert.Equal(t, filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hostname"), path)
-				return nil, errors.New("random error")
+				sandboxRootDir := filepath.Join(testRootDir, sandboxesDir, testSandboxID)
+				sandboxStateDir := filepath.Join(testStateDir, sandboxesDir, testSandboxID)
+				switch path {
+				case filepath.Join(sandboxRootDir, "hostname"), filepath.Join(sandboxRootDir, "hosts"),
+					filepath.Join(sandboxRootDir, "resolv.conf"), filepath.Join(sandboxStateDir, "shm"):
+					return nil, errors.New("random error")
+				default:
+					t.Fatalf("expected sandbox files, got: %s", path)
+				}
+				return nil, nil
 			},
 			securityContext: &runtime.LinuxContainerSecurityContext{},
-			expectedMounts: []*runtime.Mount{
-				{
-					ContainerPath:  "/etc/hosts",
-					HostPath:       filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hosts"),
-					Readonly:       false,
-					SelinuxRelabel: true,
-				},
-				{
-					ContainerPath:  resolvConfPath,
-					HostPath:       filepath.Join(testRootDir, sandboxesDir, testSandboxID, "resolv.conf"),
-					Readonly:       false,
-					SelinuxRelabel: true,
-				},
-				{
-					ContainerPath:  "/dev/shm",
-					HostPath:       filepath.Join(testStateDir, sandboxesDir, testSandboxID, "shm"),
-					Readonly:       false,
-					SelinuxRelabel: true,
-				},
-			},
+			expectedMounts:  nil,
 		},
 	} {
 		test := test