Merge pull request #33189 from bluca/fscrypt_flush

homed: flush fscrypt key on lock/deactivate

Author: bluca

src/shared/keyring-util.c renamed to src/basic/keyring-util.c

@@ -33,3 +33,34 @@ int keyring_read(key_serial_t serial, void **ret, size_t *ret_size) {
                 bufsize = (size_t) n;
         }
 }
+
+int keyring_describe(key_serial_t serial, char **ret) {
+        _cleanup_free_ char *tuple = NULL;
+        size_t sz = 64;
+        int c = -1; /* Workaround for maybe-uninitialized false positive due to missing_syscall indirection */
+
+        assert(ret);
+
+        for (;;) {
+                tuple = new(char, sz);
+                if (!tuple)
+                        return log_oom_debug();
+
+                c = keyctl(KEYCTL_DESCRIBE, serial, (unsigned long) tuple, c, 0);
+                if (c < 0)
+                        return log_debug_errno(errno, "Failed to describe key id %d: %m", serial);
+
+                if ((size_t) c <= sz)
+                        break;
+
+                sz = c;
+                free(tuple);
+        }
+
+        /* The kernel returns a final NUL in the string, verify that. */
+        assert(tuple[c-1] == 0);
+
+        *ret = TAKE_PTR(tuple);
+
+        return 0;
+}

src/shared/keyring-util.h renamed to src/basic/keyring-util.h

@@ -9,3 +9,4 @@
 #define TAKE_KEY_SERIAL(key_serial) TAKE_GENERIC(key_serial, key_serial_t, -1)
 
 int keyring_read(key_serial_t serial, void **ret, size_t *ret_size);
+int keyring_describe(key_serial_t serial, char **ret);

src/basic/meson.build

@@ -57,6 +57,7 @@ basic_sources = files(
         'lock-util.c',
         'log.c',
         'login-util.c',
+        'keyring-util.c',
         'memfd-util.c',
         'memory-util.c',
         'mempool.c',

src/home/homework-fscrypt.c

@@ -12,6 +12,7 @@
 #include "homework-fscrypt.h"
 #include "homework-mount.h"
 #include "homework-quota.h"
+#include "keyring-util.h"
 #include "memory-util.h"
 #include "missing_keyctl.h"
 #include "missing_syscall.h"
@@ -29,6 +30,98 @@
 #include "user-util.h"
 #include "xattr-util.h"
 
+static int fscrypt_unlink_key(UserRecord *h) {
+        _cleanup_free_ void *keyring = NULL;
+        size_t keyring_size = 0, n_keys = 0;
+        int r;
+
+        assert(h);
+        assert(user_record_storage(h) == USER_FSCRYPT);
+
+        r = fully_set_uid_gid(
+                        h->uid,
+                        user_record_gid(h),
+                        /* supplementary_gids= */ NULL,
+                        /* n_supplementary_gids= */ 0);
+        if (r < 0)
+                return log_error_errno(r, "Failed to change UID/GID to " UID_FMT "/" GID_FMT ": %m",
+                                       h->uid, user_record_gid(h));
+
+        r = keyring_read(KEY_SPEC_USER_KEYRING, &keyring, &keyring_size);
+        if (r < 0)
+                return log_error_errno(r, "Failed to read the keyring of user " UID_FMT ": %m", h->uid);
+
+        n_keys = keyring_size / sizeof(key_serial_t);
+        assert(keyring_size % sizeof(key_serial_t) == 0);
+
+        /* Find any key with a description starting with 'fscrypt:' and unlink it. We need to iterate as we
+         * store the key with a description that uses the hash of the secret key, that we do not have when
+         * we are deactivating. */
+        FOREACH_ARRAY(key, ((key_serial_t *) keyring), n_keys) {
+                _cleanup_free_ char *description = NULL;
+                char *d;
+
+                r = keyring_describe(*key, &description);
+                if (r < 0) {
+                        if (r == -ENOKEY) /* Something else deleted it already, that's ok. */
+                                continue;
+
+                        return log_error_errno(r, "Failed to describe key id %d: %m", *key);
+                }
+
+                /* The decription is the final element as per manpage. */
+                d = strrchr(description, ';');
+                if (!d)
+                        return log_error_errno(
+                                        SYNTHETIC_ERRNO(EINVAL),
+                                        "Failed to parse description of key id %d: %s",
+                                        *key,
+                                        description);
+
+                if (!startswith(d + 1, "fscrypt:"))
+                        continue;
+
+                r = keyctl(KEYCTL_UNLINK, *key, KEY_SPEC_USER_KEYRING, 0, 0);
+                if (r < 0) {
+                        if (errno == ENOKEY) /* Something else deleted it already, that's ok. */
+                                continue;
+
+                        return log_error_errno(
+                                        errno,
+                                        "Failed to delete encryption key with id '%d' from the keyring of user " UID_FMT ": %m",
+                                        *key,
+                                        h->uid);
+                }
+
+                log_debug("Deleted encryption key with id '%d' from the keyring of user " UID_FMT ".", *key, h->uid);
+        }
+
+        return 0;
+}
+
+int home_flush_keyring_fscrypt(UserRecord *h) {
+        int r;
+
+        assert(h);
+        assert(user_record_storage(h) == USER_FSCRYPT);
+
+        if (!uid_is_valid(h->uid))
+                return 0;
+
+        r = safe_fork("(sd-delkey)",
+                      FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_LOG|FORK_WAIT|FORK_REOPEN_LOG,
+                      NULL);
+        if (r < 0)
+                return r;
+        if (r == 0) {
+                if (fscrypt_unlink_key(h) < 0)
+                        _exit(EXIT_FAILURE);
+                _exit(EXIT_SUCCESS);
+        }
+
+        return 0;
+}
+
 static int fscrypt_upload_volume_key(
                 const uint8_t key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
                 const void *volume_key,

src/home/homework-fscrypt.h

@@ -9,3 +9,5 @@ int home_setup_fscrypt(UserRecord *h, HomeSetup *setup, const PasswordCache *cac
 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);
+
+int home_flush_keyring_fscrypt(UserRecord *h);

src/home/homework.c

@@ -379,6 +379,9 @@ static int keyring_flush(UserRecord *h) {
 
         assert(h);
 
+        if (user_record_storage(h) == USER_FSCRYPT)
+                (void) home_flush_keyring_fscrypt(h);
+
         name = strjoin("homework-user-", h->user_name);
         if (!name)
                 return log_oom();

src/libsystemd/sd-id128/sd-id128.c

@@ -13,6 +13,7 @@
 #include "hmac.h"
 #include "id128-util.h"
 #include "io-util.h"
+#include "keyring-util.h"
 #include "macro.h"
 #include "missing_syscall.h"
 #include "missing_threads.h"
@@ -202,7 +203,6 @@ static int get_invocation_from_keyring(sd_id128_t *ret) {
         char *d, *p, *g, *u, *e;
         unsigned long perms;
         key_serial_t key;
-        size_t sz = 256;
         uid_t uid;
         gid_t gid;
         int r, c;
@@ -221,24 +221,9 @@ static int get_invocation_from_keyring(sd_id128_t *ret) {
                 return -errno;
         }
 
-        for (;;) {
-                description = new(char, sz);
-                if (!description)
-                        return -ENOMEM;
-
-                c = keyctl(KEYCTL_DESCRIBE, key, (unsigned long) description, sz, 0);
-                if (c < 0)
-                        return -errno;
-
-                if ((size_t) c <= sz)
-                        break;
-
-                sz = c;
-                free(description);
-        }
-
-        /* The kernel returns a final NUL in the string, verify that. */
-        assert(description[c-1] == 0);
+        r = keyring_describe(key, &description);
+        if (r < 0)
+                return r;
 
         /* Chop off the final description string */
         d = strrchr(description, ';');

src/shared/meson.build

@@ -100,7 +100,6 @@ shared_sources = files(
         'kbd-util.c',
         'kernel-config.c',
         'kernel-image.c',
-        'keyring-util.c',
         'killall.c',
         'label-util.c',
         'libarchive-util.c',