Merge pull request #21161 from poettering/homed-uidmap-fscrypt

homed: teach the fscrypt backend uidmap too

src/home/homework-directory.c

@@ -241,13 +241,9 @@ int home_create_directory_or_subvolume(UserRecord *h, HomeSetup *setup, UserReco
         setup->root_fd = safe_close(setup->root_fd);
 
         /* Unmount mapped mount before we move the dir into place */
-        if (setup->undo_mount) {
-                r = umount_verbose(LOG_ERR, HOME_RUNTIME_WORK_DIR, UMOUNT_NOFOLLOW);
-                if (r < 0)
-                        return r;
-
-                setup->undo_mount = false;
-        }
+        r = home_setup_undo_mount(setup, LOG_ERR);
+        if (r < 0)
+                return r;
 
         if (rename(temporary, ip) < 0)
                 return log_error_errno(errno, "Failed to rename %s to %s: %m", temporary, ip);

src/home/homework-fscrypt.c

@@ -10,11 +10,13 @@
 #include "fd-util.h"
 #include "hexdecoct.h"
 #include "homework-fscrypt.h"
+#include "homework-mount.h"
 #include "homework-quota.h"
 #include "memory-util.h"
 #include "missing_keyctl.h"
 #include "missing_syscall.h"
 #include "mkdir.h"
+#include "mount-util.h"
 #include "nulstr-util.h"
 #include "openssl-util.h"
 #include "parse-util.h"
@@ -290,8 +292,9 @@ int home_setup_fscrypt(
         int r;
 
         assert(h);
-        assert(setup);
         assert(user_record_storage(h) == USER_FSCRYPT);
+        assert(setup);
+        assert(setup->root_fd < 0);
 
         assert_se(ip = user_record_image_path(h));
 
@@ -361,6 +364,33 @@ int home_setup_fscrypt(
                 }
         }
 
+        /* We'll bind mount the image directory to a new mount point where we'll start adjusting it. Only
+         * once that's complete we'll move the thing to its final place eventually. */
+        r = home_unshare_and_mkdir();
+        if (r < 0)
+                return r;
+
+        r = mount_follow_verbose(LOG_ERR, ip, HOME_RUNTIME_WORK_DIR, NULL, MS_BIND, NULL);
+        if (r < 0)
+                return r;
+
+        setup->undo_mount = true;
+
+        /* Turn off any form of propagation for this */
+        r = mount_nofollow_verbose(LOG_ERR, NULL, HOME_RUNTIME_WORK_DIR, NULL, MS_PRIVATE, NULL);
+        if (r < 0)
+                return r;
+
+        /* Adjust MS_SUID and similar flags */
+        r = mount_nofollow_verbose(LOG_ERR, NULL, HOME_RUNTIME_WORK_DIR, NULL, MS_BIND|MS_REMOUNT|user_record_mount_flags(h), NULL);
+        if (r < 0)
+                return r;
+
+        safe_close(setup->root_fd);
+        setup->root_fd = open(HOME_RUNTIME_WORK_DIR, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW);
+        if (setup->root_fd < 0)
+                return log_error_errno(errno, "Failed to open home directory: %m");
+
         return 0;
 }
 
@@ -456,15 +486,16 @@ finish:
 
 int home_create_fscrypt(
                 UserRecord *h,
+                HomeSetup *setup,
                 char **effective_passwords,
                 UserRecord **ret_home) {
 
         _cleanup_(rm_rf_physical_and_freep) char *temporary = NULL;
         _cleanup_(user_record_unrefp) UserRecord *new_home = NULL;
         _cleanup_(erase_and_freep) void *volume_key = NULL;
+        _cleanup_close_ int mount_fd = -1;
         struct fscrypt_policy policy = {};
         size_t volume_key_size = 512 / 8;
-        _cleanup_close_ int root_fd = -1;
         _cleanup_free_ char *d = NULL;
         uint32_t nr = 0;
         const char *ip;
@@ -473,6 +504,7 @@ int home_create_fscrypt(
 
         assert(h);
         assert(user_record_storage(h) == USER_FSCRYPT);
+        assert(setup);
         assert(ret_home);
 
         assert_se(ip = user_record_image_path(h));
@@ -488,11 +520,15 @@ int home_create_fscrypt(
 
         temporary = TAKE_PTR(d); /* Needs to be destroyed now */
 
-        root_fd = open(temporary, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW);
-        if (root_fd < 0)
+        r = home_unshare_and_mkdir();
+        if (r < 0)
+                return r;
+
+        setup->root_fd = open(temporary, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW);
+        if (setup->root_fd < 0)
                 return log_error_errno(errno, "Failed to open temporary home directory: %m");
 
-        if (ioctl(root_fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) < 0) {
+        if (ioctl(setup->root_fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) < 0) {
                 if (ERRNO_IS_NOT_SUPPORTED(errno)) {
                         log_error_errno(errno, "File system does not support fscrypt: %m");
                         return -ENOLINK; /* make recognizable */
@@ -526,13 +562,13 @@ int home_create_fscrypt(
 
         log_info("Uploaded volume key to kernel.");
 
-        if (ioctl(root_fd, FS_IOC_SET_ENCRYPTION_POLICY, &policy) < 0)
+        if (ioctl(setup->root_fd, FS_IOC_SET_ENCRYPTION_POLICY, &policy) < 0)
                 return log_error_errno(errno, "Failed to set fscrypt policy on directory: %m");
 
         log_info("Encryption policy set.");
 
         STRV_FOREACH(i, effective_passwords) {
-                r = fscrypt_slot_set(root_fd, volume_key, volume_key_size, *i, nr);
+                r = fscrypt_slot_set(setup->root_fd, volume_key, volume_key_size, *i, nr);
                 if (r < 0)
                         return r;
 
@@ -541,11 +577,26 @@ int home_create_fscrypt(
 
         (void) home_update_quota_classic(h, temporary);
 
-        r = home_populate(h, root_fd);
+        r = home_shift_uid(setup->root_fd, HOME_RUNTIME_WORK_DIR, h->uid, h->uid, &mount_fd);
+        if (r > 0)
+                setup->undo_mount = true; /* If uidmaps worked we have a mount to undo again */
+
+        if (mount_fd >= 0) {
+                /* If we have established a new mount, then we can use that as new root fd to our home directory. */
+                safe_close(setup->root_fd);
+
+                setup->root_fd = fd_reopen(mount_fd, O_RDONLY|O_CLOEXEC|O_DIRECTORY);
+                if (setup->root_fd < 0)
+                        return log_error_errno(setup->root_fd, "Unable to convert mount fd into proper directory fd: %m");
+
+                mount_fd = safe_close(mount_fd);
+        }
+
+        r = home_populate(h, setup->root_fd);
         if (r < 0)
                 return r;
 
-        r = home_sync_and_statfs(root_fd, NULL);
+        r = home_sync_and_statfs(setup->root_fd, NULL);
         if (r < 0)
                 return r;
 
@@ -570,6 +621,12 @@ int home_create_fscrypt(
         if (r < 0)
                 return log_error_errno(r, "Failed to add binding to record: %m");
 
+        setup->root_fd = safe_close(setup->root_fd);
+
+        r = home_setup_undo_mount(setup, LOG_ERR);
+        if (r < 0)
+                return r;
+
         if (rename(temporary, ip) < 0)
                 return log_error_errno(errno, "Failed to rename %s to %s: %m", temporary, ip);
 
@@ -635,7 +692,6 @@ int home_passwd_fscrypt(
                         continue;
 
                 if (fremovexattr(setup->root_fd, xa) < 0)
-
                         if (errno != ENODATA)
                                 log_warning_errno(errno, "Failed to remove xattr %s: %m", xa);
         }

src/home/homework-fscrypt.h

@@ -5,6 +5,7 @@
 #include "user-record.h"
 
 int home_setup_fscrypt(UserRecord *h, const PasswordCache *cache, HomeSetup *setup);
-int home_create_fscrypt(UserRecord *h, char **effective_passwords, UserRecord **ret_home);
+
+int home_create_fscrypt(UserRecord *h, HomeSetup *setup, char **effective_passwords, UserRecord **ret_home);
 
 int home_passwd_fscrypt(UserRecord *h, HomeSetup *setup, const PasswordCache *cache, char **effective_passwords);

src/home/homework.c

@@ -298,6 +298,22 @@ static void drop_caches_now(void) {
                 log_debug("Dropped caches.");
 }
 
+int home_setup_undo_mount(HomeSetup *setup, int level) {
+        int r;
+
+        assert(setup);
+
+        if (!setup->undo_mount)
+                return 0;
+
+        r = umount_verbose(level, HOME_RUNTIME_WORK_DIR, UMOUNT_NOFOLLOW);
+        if (r < 0)
+                return r;
+
+        setup->undo_mount = false;
+        return 1;
+}
+
 int home_setup_done(HomeSetup *setup) {
         int r = 0, q;
 
@@ -316,11 +332,9 @@ int home_setup_done(HomeSetup *setup) {
                 setup->root_fd = safe_close(setup->root_fd);
         }
 
-        if (setup->undo_mount) {
-                q = umount_verbose(LOG_DEBUG, HOME_RUNTIME_WORK_DIR, UMOUNT_NOFOLLOW);
-                if (q < 0)
-                        r = q;
-        }
+        q = home_setup_undo_mount(setup, LOG_DEBUG);
+        if (q < 0)
+                r = q;
 
         if (setup->undo_dm && setup->crypt_device && setup->dm_name) {
                 q = sym_crypt_deactivate_by_name(setup->crypt_device, setup->dm_name, 0);
@@ -1272,7 +1286,7 @@ static int home_create(UserRecord *h, UserRecord **ret_home) {
                 break;
 
         case USER_FSCRYPT:
-                r = home_create_fscrypt(h, effective_passwords, &new_home);
+                r = home_create_fscrypt(h, &setup, effective_passwords, &new_home);
                 break;
 
         case USER_CIFS:

src/home/homework.h

@@ -70,6 +70,8 @@ typedef enum HomeSetupFlags {
 
 int home_setup_done(HomeSetup *setup);
 
+int home_setup_undo_mount(HomeSetup *setup, int level);
+
 int home_setup(UserRecord *h, HomeSetupFlags flags, PasswordCache *cache, HomeSetup *setup, UserRecord **ret_header_home);
 
 int home_refresh(UserRecord *h, HomeSetup *setup, UserRecord *header_home, PasswordCache *cache, struct statfs *ret_statfs, UserRecord **ret_new_home);