| // Copyright (c) 2013 The Chromium OS Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "cros-disks/fuse_mounter.h" |
| |
| #include <linux/capability.h> |
| #include <sys/mount.h> |
| #include <sys/stat.h> |
| #include <sys/types.h> |
| #include <unistd.h> |
| |
| #include <memory> |
| #include <string> |
| |
| #include <base/macros.h> |
| #include <base/bind.h> |
| #include <base/callback_helpers.h> |
| #include <base/files/file.h> |
| #include <base/logging.h> |
| #include <base/strings/stringprintf.h> |
| #include <base/strings/string_util.h> |
| |
| #include "cros-disks/platform.h" |
| #include "cros-disks/sandboxed_process.h" |
| |
| using std::string; |
| |
| namespace cros_disks { |
| |
| namespace { |
| |
| const mode_t kSourcePathPermissions = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP; |
| const mode_t kTargetPathPermissions = S_IRWXU | S_IRWXG; |
| |
| const char kFuseDeviceFile[] = "/dev/fuse"; |
| const MountOptions::Flags kRequiredFuseMountFlags = |
| MS_NODEV | MS_NOEXEC | MS_NOSUID; |
| |
| MountErrorType ConfigureCommonSandbox(SandboxedProcess* sandbox, |
| const Platform* platform, |
| bool network_ns, |
| const base::FilePath& seccomp, |
| bool unprivileged) { |
| // TODO(crbug.com/866377): Run FUSE fully deprivileged. |
| // Currently SYS_ADMIN is needed to perform mount()/umount() calls from |
| // libfuse. |
| uint64_t capabilities = unprivileged ? 0 : CAP_TO_MASK(CAP_SYS_ADMIN); |
| sandbox->SetCapabilities(capabilities); |
| sandbox->SetNoNewPrivileges(); |
| |
| // The FUSE mount program is put under a new mount namespace, so mounts |
| // inside that namespace don't normally propagate out except when a mount is |
| // created under /media, which is marked as a shared mount (by |
| // chromeos_startup). This prevents the FUSE mount program from remounting an |
| // existing mount point outside /media. |
| // |
| // TODO(benchan): It's fragile to assume chromeos_startup makes /media a |
| // shared mount. cros-disks should verify that and make /media a shared mount |
| // when necessary. |
| sandbox->NewMountNamespace(); |
| |
| // Prevent minjail from turning /media private again. |
| // |
| // TODO(benchan): Revisit this once minijail provides a finer control over |
| // what should be remounted private and what can remain shared (b:62056108). |
| sandbox->SkipRemountPrivate(); |
| |
| // TODO(benchan): Re-enable cgroup namespace when either Chrome OS |
| // kernel 3.8 supports it or no more supported devices use kernel |
| // 3.8. |
| // mount_process.NewCgroupNamespace(); |
| |
| sandbox->NewIpcNamespace(); |
| |
| if (network_ns) { |
| sandbox->NewNetworkNamespace(); |
| } |
| |
| if (!seccomp.empty()) { |
| if (!platform->PathExists(seccomp.value())) { |
| LOG(ERROR) << "Seccomp policy '" << seccomp.value() << "' is missing"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| sandbox->LoadSeccompFilterPolicy(seccomp.value()); |
| } |
| |
| // Prepare mounts for pivot_root. |
| if (!sandbox->SetUpMinimalMounts()) { |
| LOG(ERROR) << "Can't set up minijail mounts"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| |
| if (!unprivileged) { |
| // Bind the FUSE device file. |
| if (!sandbox->BindMount(kFuseDeviceFile, kFuseDeviceFile, true, false)) { |
| LOG(ERROR) << "Unable to bind FUSE device file"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| |
| // Mounts are exposed to the rest of the system through this shared mount. |
| if (!sandbox->BindMount("/media", "/media", true, false)) { |
| LOG(ERROR) << "Can't bind /media"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| } |
| |
| // Data dirs if any are mounted inside /run/fuse. |
| if (!sandbox->Mount("tmpfs", "/run", "tmpfs", "mode=0755,size=10M")) { |
| LOG(ERROR) << "Can't mount /run"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| if (!sandbox->BindMount("/run/fuse", "/run/fuse", false, false)) { |
| LOG(ERROR) << "Can't bind /run/fuse"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| |
| if (!network_ns) { |
| // Network DNS configs are in /run/shill. |
| if (!sandbox->BindMount("/run/shill", "/run/shill", false, false)) { |
| LOG(ERROR) << "Can't bind /run/shill"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| // Hardcoded hosts are mounted into /etc/hosts.d when Crostini is enabled. |
| if (platform->PathExists("/etc/hosts.d") && |
| !sandbox->BindMount("/etc/hosts.d", "/etc/hosts.d", false, false)) { |
| LOG(ERROR) << "Can't bind /etc/hosts.d"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| } |
| if (!sandbox->EnterPivotRoot()) { |
| LOG(ERROR) << "Can't pivot root"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| |
| return MountErrorType::MOUNT_ERROR_NONE; |
| } |
| |
| bool MountFuseDevice(const Platform* platform, |
| const std::string& source, |
| const base::FilePath& target, |
| const base::File& fuse_file, |
| uid_t mount_user_id, |
| gid_t mount_group_id, |
| const MountOptions& options) { |
| // Mount options for FUSE: |
| // fd - File descriptor for /dev/fuse. |
| // user_id/group_id - user/group for file access control. Essentially |
| // bypassed due to allow_other, but still required to be set. |
| // allow_other - Allows users other than user_id/group_id to access files |
| // on the file system. By default, FUSE prevents any process other than |
| // ones running under user_id/group_id to access files, regardless of |
| // the file's permissions. |
| // default_permissions - Enforce permission checking. |
| // rootmode - Mode bits for the root inode. |
| std::string fuse_mount_options = base::StringPrintf( |
| "fd=%d,user_id=%u,group_id=%u,allow_other,default_permissions," |
| "rootmode=%o", |
| fuse_file.GetPlatformFile(), mount_user_id, mount_group_id, S_IFDIR); |
| |
| // "nosymfollow" is a special mount option that's passed to the Chromium LSM |
| // and not forwarded to the FUSE driver. If it's set, add it as a mount |
| // option. |
| if (options.HasOption(MountOptions::kOptionNoSymFollow)) { |
| fuse_mount_options.append(","); |
| fuse_mount_options.append(MountOptions::kOptionNoSymFollow); |
| } |
| |
| std::string fuse_type = "fuse"; |
| struct stat statbuf = {0}; |
| if (stat(source.c_str(), &statbuf) == 0 && S_ISBLK(statbuf.st_mode)) { |
| LOG(INFO) << "Source file " << source << " is a block device."; |
| // TODO(crbug.com/931500): Determine and set blksize mount option. Default |
| // is 512, which works everywhere, but is not necessarily optimal. Any |
| // power-of-2 in the range [512, PAGE_SIZE] will work, but the optimal size |
| // is the block/cluster size of the file system. |
| fuse_type = "fuseblk"; |
| } |
| |
| auto flags = options.ToMountFlagsAndData().first; |
| |
| return platform->Mount(source, target.value(), fuse_type, |
| flags | kRequiredFuseMountFlags, fuse_mount_options) == |
| MountErrorType::MOUNT_ERROR_NONE; |
| } |
| |
| } // namespace |
| |
| FUSEMounter::FUSEMounter(const string& source_path, |
| const string& target_path, |
| const string& filesystem_type, |
| const MountOptions& mount_options, |
| const Platform* platform, |
| const string& mount_program_path, |
| const string& mount_user, |
| const std::string& seccomp_policy, |
| const std::vector<BindPath>& accessible_paths, |
| bool permit_network_access, |
| bool unprivileged_mount, |
| const std::string& mount_group) |
| : MounterCompat(filesystem_type, |
| source_path, |
| base::FilePath(target_path), |
| mount_options), |
| platform_(platform), |
| mount_program_path_(mount_program_path), |
| mount_user_(mount_user), |
| mount_group_(mount_group), |
| seccomp_policy_(seccomp_policy), |
| accessible_paths_(accessible_paths), |
| permit_network_access_(permit_network_access), |
| unprivileged_mount_(unprivileged_mount) {} |
| |
| MountErrorType FUSEMounter::MountImpl() const { |
| auto mount_process = CreateSandboxedProcess(); |
| auto status = ConfigureCommonSandbox( |
| mount_process.get(), platform_, !permit_network_access_, |
| base::FilePath(seccomp_policy_), unprivileged_mount_); |
| if (status != MountErrorType::MOUNT_ERROR_NONE) { |
| return status; |
| } |
| |
| uid_t mount_user_id; |
| gid_t mount_group_id; |
| if (!platform_->GetUserAndGroupId(mount_user_, &mount_user_id, |
| &mount_group_id)) { |
| LOG(ERROR) << "Can't resolve user '" << mount_user_ << "'"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| if (!mount_group_.empty() && |
| !platform_->GetGroupId(mount_group_, &mount_group_id)) { |
| return MOUNT_ERROR_INTERNAL; |
| } |
| |
| mount_process->SetUserId(mount_user_id); |
| mount_process->SetGroupId(mount_group_id); |
| |
| if (!platform_->PathExists(mount_program_path_)) { |
| LOG(ERROR) << "Mount program '" << mount_program_path_ << "' not found."; |
| return MountErrorType::MOUNT_ERROR_MOUNT_PROGRAM_NOT_FOUND; |
| } |
| mount_process->AddArgument(mount_program_path_); |
| |
| base::ScopedClosureRunner fuse_failure_unmounter; |
| base::File fuse_file; |
| if (unprivileged_mount_) { |
| LOG(INFO) << "Using deprivileged FUSE with fd passing."; |
| |
| fuse_file = base::File( |
| base::FilePath(kFuseDeviceFile), |
| base::File::FLAG_OPEN | base::File::FLAG_READ | base::File::FLAG_WRITE); |
| if (!fuse_file.IsValid()) { |
| LOG(ERROR) << "Unable to open FUSE device file. Error: " |
| << fuse_file.error_details() << " " |
| << base::File::ErrorToString(fuse_file.error_details()); |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| |
| if (!MountFuseDevice(platform_, source(), base::FilePath(target_path()), |
| fuse_file, mount_user_id, mount_group_id, |
| mount_options())) { |
| LOG(ERROR) << "Can't perform unprivileged FUSE mount"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| |
| // Unmount the FUSE filesystem if any later part fails. |
| fuse_failure_unmounter.ReplaceClosure(base::Bind( |
| [](const Platform* platform, const std::string& target_path) { |
| if (!platform->Unmount(target_path, 0)) { |
| LOG(ERROR) << "Failed to unmount " << target_path |
| << " on deprivileged fuse mount failure."; |
| } |
| }, |
| platform_, target_path().value())); |
| } else { |
| // To perform a non-root mount via the FUSE mount program, change the |
| // group of the source and target path to the group of the non-privileged |
| // user, but keep the user of the source and target path unchanged. Also set |
| // appropriate group permissions on the source and target path. |
| if (!platform_->SetOwnership(target_path().value(), getuid(), |
| mount_group_id) || |
| !platform_->SetPermissions(target_path().value(), |
| kTargetPathPermissions)) { |
| LOG(ERROR) << "Can't set up permissions on the mount point"; |
| return MountErrorType::MOUNT_ERROR_INSUFFICIENT_PERMISSIONS; |
| } |
| } |
| |
| // Source might be an URI. Only try to re-own source if it looks like |
| // an existing path. |
| if (!source().empty() && platform_->PathExists(source())) { |
| if (!platform_->SetOwnership(source(), getuid(), mount_group_id) || |
| !platform_->SetPermissions(source(), kSourcePathPermissions)) { |
| LOG(ERROR) << "Can't set up permissions on the source"; |
| return MountErrorType::MOUNT_ERROR_INSUFFICIENT_PERMISSIONS; |
| } |
| } |
| |
| // If a block device is being mounted, bind mount it into the sandbox. |
| if (base::StartsWith(source(), "/dev/", base::CompareCase::SENSITIVE)) { |
| if (!mount_process->BindMount(source(), source(), true, false)) { |
| LOG(ERROR) << "Unable to bind mount device " << source(); |
| return MountErrorType::MOUNT_ERROR_INVALID_ARGUMENT; |
| } |
| } |
| |
| // TODO(crbug.com/933018): Remove when DriveFS helper is refactored. |
| if (!mount_process->Mount("tmpfs", "/home", "tmpfs", "mode=0755,size=10M")) { |
| LOG(ERROR) << "Can't mount /home"; |
| return MountErrorType::MOUNT_ERROR_INTERNAL; |
| } |
| |
| // This is for additional data dirs. |
| for (const auto& path : accessible_paths_) { |
| if (!mount_process->BindMount(path.path, path.path, path.writable, |
| path.recursive)) { |
| LOG(ERROR) << "Can't bind " << path.path; |
| return MountErrorType::MOUNT_ERROR_INVALID_ARGUMENT; |
| } |
| } |
| |
| string options_string = mount_options().ToString(); |
| if (!options_string.empty()) { |
| mount_process->AddArgument("-o"); |
| mount_process->AddArgument(options_string); |
| } |
| if (!source().empty()) { |
| mount_process->AddArgument(source()); |
| } |
| if (unprivileged_mount_) { |
| mount_process->AddArgument( |
| base::StringPrintf("/dev/fd/%d", fuse_file.GetPlatformFile())); |
| } else { |
| mount_process->AddArgument(target_path().value()); |
| } |
| |
| int return_code = mount_process->Run(); |
| if (return_code != 0) { |
| LOG(WARNING) << "FUSE mount program failed with a return code " |
| << return_code; |
| return MountErrorType::MOUNT_ERROR_MOUNT_PROGRAM_FAILED; |
| } |
| // The |fuse_failure_unmounter| closure runner is used to unmount the FUSE |
| // filesystem (for unprivileged mounts) if any part of starting the FUSE |
| // helper process fails. At this point, the process has successfully started, |
| // so release the closure runner to prevent the FUSE mount point from being |
| // unmounted. |
| ignore_result(fuse_failure_unmounter.Release()); |
| return MountErrorType::MOUNT_ERROR_NONE; |
| } |
| |
| std::unique_ptr<SandboxedProcess> FUSEMounter::CreateSandboxedProcess() const { |
| return std::make_unique<SandboxedProcess>(); |
| } |
| |
| } // namespace cros_disks |
