Merge tag 'keys-request-20190626' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull request_key improvements from David Howells:
 "These are all request_key()-related, including a fix and some improvements:

   - Fix the lack of a Link permission check on a key found by
     request_key(), thereby enabling request_key() to link keys that
     don't grant this permission to the target keyring (which must still
     grant Write permission).

     Note that the key must be in the caller's keyrings already to be
     found.

   - Invalidate used request_key authentication keys rather than
     revoking them, so that they get cleaned up immediately rather than
     hanging around till the expiry time is passed.

   - Move the RCU locks outwards from the keyring search functions so
     that a request_key_rcu() can be provided. This can be called in RCU
     mode, so it can't sleep and can't upcall - but it can be called
     from LOOKUP_RCU pathwalk mode.

   - Cache the latest positive result of request_key*() temporarily in
     task_struct so that filesystems that make a lot of request_key()
     calls during pathwalk can take advantage of it to avoid having to
     redo the searching. This requires CONFIG_KEYS_REQUEST_CACHE=y.

     It is assumed that the key just found is likely to be used multiple
     times in each step in an RCU pathwalk, and is likely to be reused
     for the next step too.

     Note that the cleanup of the cache is done on TIF_NOTIFY_RESUME,
     just before userspace resumes, and on exit"

* tag 'keys-request-20190626' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  keys: Kill off request_key_async{,_with_auxdata}
  keys: Cache result of request_key*() temporarily in task_struct
  keys: Provide request_key_rcu()
  keys: Move the RCU locks outwards from the keyring search functions
  keys: Invalidate used request_key authentication keys
  keys: Fix request_key() lack of Link perm check on found key

8 files changed, 180 insertions, 106 deletions

diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index ee502e4d390b..dd313438fecf 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -25,6 +25,24 @@ config KEYS_COMPAT
         def_bool y
         depends on COMPAT && KEYS
 
+config KEYS_REQUEST_CACHE
+        bool "Enable temporary caching of the last request_key() result"
+        depends on KEYS
+        help
+          This option causes the result of the last successful request_key()
+          call that didn't upcall to the kernel to be cached temporarily in the
+          task_struct.  The cache is cleared by exit and just prior to the
+          resumption of userspace.
+
+          This allows the key used for multiple step processes where each step
+          wants to request a key that is likely the same as the one requested
+          by the last step to save on the searching.
+
+          An example of such a process is a pathwalk through a network
+          filesystem in which each method needs to request an authentication
+          key.  Pathwalk will call multiple methods for each dentry traversed
+          (permission, d_revalidate, lookup, getxattr, getacl, ...).
+
 config PERSISTENT_KEYRINGS
         bool "Enable register of persistent per-UID keyrings"
         depends on KEYS
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 0f48b53754b3..663f291e30d4 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -135,11 +135,11 @@ struct keyring_search_context {
 
 extern bool key_default_cmp(const struct key *key,
                             const struct key_match_data *match_data);
-extern key_ref_t keyring_search_aux(key_ref_t keyring_ref,
+extern key_ref_t keyring_search_rcu(key_ref_t keyring_ref,
                                     struct keyring_search_context *ctx);
 
-extern key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx);
-extern key_ref_t search_process_keyrings(struct keyring_search_context *ctx);
+extern key_ref_t search_cred_keyrings_rcu(struct keyring_search_context *ctx);
+extern key_ref_t search_process_keyrings_rcu(struct keyring_search_context *ctx);
 
 extern struct key *find_keyring_by_name(const char *name, bool uid_keyring);
 
diff --git a/security/keys/key.c b/security/keys/key.c
index d3c17d76ea76..85dddc0190a7 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -455,7 +455,7 @@ static int __key_instantiate_and_link(struct key *key,
 
                         /* disable the authorisation key */
                         if (authkey)
-                                key_revoke(authkey);
+                                key_invalidate(authkey);
 
                         if (prep->expiry != TIME64_MAX) {
                                 key->expiry = prep->expiry;
@@ -612,7 +612,7 @@ int key_reject_and_link(struct key *key,
 
                 /* disable the authorisation key */
                 if (authkey)
-                        key_revoke(authkey);
+                        key_invalidate(authkey);
         }
 
         mutex_unlock(&key_construction_mutex);
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 204b5a4d180e..e4de4070c754 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -831,7 +831,7 @@ found:
 }
 
 /**
- * keyring_search_aux - Search a keyring tree for a key matching some criteria
+ * keyring_search_rcu - Search a keyring tree for a matching key under RCU
  * @keyring_ref: A pointer to the keyring with possession indicator.
  * @ctx: The keyring search context.
  *
@@ -843,7 +843,9 @@ found:
  * addition, the LSM gets to forbid keyring searches and key matches.
  *
  * The search is performed as a breadth-then-depth search up to the prescribed
- * limit (KEYRING_SEARCH_MAX_DEPTH).
+ * limit (KEYRING_SEARCH_MAX_DEPTH).  The caller must hold the RCU read lock to
+ * prevent keyrings from being destroyed or rearranged whilst they are being
+ * searched.
  *
  * Keys are matched to the type provided and are then filtered by the match
  * function, which is given the description to use in any way it sees fit.  The
@@ -862,7 +864,7 @@ found:
  * In the case of a successful return, the possession attribute from
  * @keyring_ref is propagated to the returned key reference.
  */
-key_ref_t keyring_search_aux(key_ref_t keyring_ref,
+key_ref_t keyring_search_rcu(key_ref_t keyring_ref,
                              struct keyring_search_context *ctx)
 {
         struct key *keyring;
@@ -884,11 +886,9 @@ key_ref_t keyring_search_aux(key_ref_t keyring_ref,
                         return ERR_PTR(err);
         }
 
-        rcu_read_lock();
         ctx->now = ktime_get_real_seconds();
         if (search_nested_keyrings(keyring, ctx))
                 __key_get(key_ref_to_ptr(ctx->result));
-        rcu_read_unlock();
         return ctx->result;
 }
 
@@ -898,7 +898,7 @@ key_ref_t keyring_search_aux(key_ref_t keyring_ref,
  * @type: The type of keyring we want to find.
  * @description: The name of the keyring we want to find.
  *
- * As keyring_search_aux() above, but using the current task's credentials and
+ * As keyring_search_rcu() above, but using the current task's credentials and
  * type's default matching function and preferred search method.
  */
 key_ref_t keyring_search(key_ref_t keyring,
@@ -924,7 +924,9 @@ key_ref_t keyring_search(key_ref_t keyring,
                         return ERR_PTR(ret);
         }
 
-        key = keyring_search_aux(keyring, &ctx);
+        rcu_read_lock();
+        key = keyring_search_rcu(keyring, &ctx);
+        rcu_read_unlock();
 
         if (type->match_free)
                 type->match_free(&ctx.match_data);
diff --git a/security/keys/proc.c b/security/keys/proc.c
index 4e3266a2529e..7f15550c10f5 100644
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -175,7 +175,9 @@ static int proc_keys_show(struct seq_file *m, void *v)
          * skip if the key does not indicate the possessor can view it
          */
         if (key->perm & KEY_POS_VIEW) {
-                skey_ref = search_my_process_keyrings(&ctx);
+                rcu_read_lock();
+                skey_ref = search_cred_keyrings_rcu(&ctx);
+                rcu_read_unlock();
                 if (!IS_ERR(skey_ref)) {
                         key_ref_put(skey_ref);
                         key_ref = make_key_ref(key, 1);
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index a40b33614208..b99ad2c5342f 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -314,7 +314,8 @@ void key_fsgid_changed(struct cred *new_cred)
 
 /*
  * Search the process keyrings attached to the supplied cred for the first
- * matching key.
+ * matching key under RCU conditions (the caller must be holding the RCU read
+ * lock).
  *
  * The search criteria are the type and the match function.  The description is
  * given to the match function as a parameter, but doesn't otherwise influence
@@ -333,7 +334,7 @@ void key_fsgid_changed(struct cred *new_cred)
  * In the case of a successful return, the possession attribute is set on the
  * returned key reference.
  */
-key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
+key_ref_t search_cred_keyrings_rcu(struct keyring_search_context *ctx)
 {
         key_ref_t key_ref, ret, err;
         const struct cred *cred = ctx->cred;
@@ -351,7 +352,7 @@ key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
 
         /* search the thread keyring first */
         if (cred->thread_keyring) {
-                key_ref = keyring_search_aux(
+                key_ref = keyring_search_rcu(
                         make_key_ref(cred->thread_keyring, 1), ctx);
                 if (!IS_ERR(key_ref))
                         goto found;
@@ -369,7 +370,7 @@ key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
 
         /* search the process keyring second */
         if (cred->process_keyring) {
-                key_ref = keyring_search_aux(
+                key_ref = keyring_search_rcu(
                         make_key_ref(cred->process_keyring, 1), ctx);
                 if (!IS_ERR(key_ref))
                         goto found;
@@ -390,7 +391,7 @@ key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
 
         /* search the session keyring */
         if (cred->session_keyring) {
-                key_ref = keyring_search_aux(
+                key_ref = keyring_search_rcu(
                         make_key_ref(cred->session_keyring, 1), ctx);
 
                 if (!IS_ERR(key_ref))
@@ -411,7 +412,7 @@ key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
         }
         /* or search the user-session keyring */
         else if (READ_ONCE(cred->user->session_keyring)) {
-                key_ref = keyring_search_aux(
+                key_ref = keyring_search_rcu(
                         make_key_ref(READ_ONCE(cred->user->session_keyring), 1),
                         ctx);
                 if (!IS_ERR(key_ref))
@@ -444,16 +445,16 @@ found:
  * the keys attached to the assumed authorisation key using its credentials if
  * one is available.
  *
- * Return same as search_my_process_keyrings().
+ * The caller must be holding the RCU read lock.
+ *
+ * Return same as search_cred_keyrings_rcu().
  */
-key_ref_t search_process_keyrings(struct keyring_search_context *ctx)
+key_ref_t search_process_keyrings_rcu(struct keyring_search_context *ctx)
 {
         struct request_key_auth *rka;
         key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;
 
-        might_sleep();
-
-        key_ref = search_my_process_keyrings(ctx);
+        key_ref = search_cred_keyrings_rcu(ctx);
         if (!IS_ERR(key_ref))
                 goto found;
         err = key_ref;
@@ -468,24 +469,17 @@ key_ref_t search_process_keyrings(struct keyring_search_context *ctx)
             ) {
                 const struct cred *cred = ctx->cred;
 
-                /* defend against the auth key being revoked */
-                down_read(&cred->request_key_auth->sem);
-
-                if (key_validate(ctx->cred->request_key_auth) == 0) {
+                if (key_validate(cred->request_key_auth) == 0) {
                         rka = ctx->cred->request_key_auth->payload.data[0];
 
+                        //// was search_process_keyrings() [ie. recursive]
                         ctx->cred = rka->cred;
-                        key_ref = search_process_keyrings(ctx);
+                        key_ref = search_cred_keyrings_rcu(ctx);
                         ctx->cred = cred;
 
-                        up_read(&cred->request_key_auth->sem);
-
                         if (!IS_ERR(key_ref))
                                 goto found;
-
                         ret = key_ref;
-                } else {
-                        up_read(&cred->request_key_auth->sem);
                 }
         }
 
@@ -500,7 +494,6 @@ key_ref_t search_process_keyrings(struct keyring_search_context *ctx)
 found:
         return key_ref;
 }
-
 /*
  * See if the key we're looking at is the target key.
  */
@@ -687,7 +680,9 @@ try_again:
                 ctx.index_key                   = key->index_key;
                 ctx.match_data.raw_data         = key;
                 kdebug("check possessed");
-                skey_ref = search_process_keyrings(&ctx);
+                rcu_read_lock();
+                skey_ref = search_process_keyrings_rcu(&ctx);
+                rcu_read_unlock();
                 kdebug("possessed=%p", skey_ref);
 
                 if (!IS_ERR(skey_ref)) {
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index fcef7e26b94b..f2b4da143963 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -18,6 +18,31 @@
 
 #define key_negative_timeout    60      /* default timeout on a negative key's existence */
 
+static struct key *check_cached_key(struct keyring_search_context *ctx)
+{
+#ifdef CONFIG_KEYS_REQUEST_CACHE
+        struct key *key = current->cached_requested_key;
+
+        if (key &&
+            ctx->match_data.cmp(key, &ctx->match_data) &&
+            !(key->flags & ((1 << KEY_FLAG_INVALIDATED) |
+                            (1 << KEY_FLAG_REVOKED))))
+                return key_get(key);
+#endif
+        return NULL;
+}
+
+static void cache_requested_key(struct key *key)
+{
+#ifdef CONFIG_KEYS_REQUEST_CACHE
+        struct task_struct *t = current;
+
+        key_put(t->cached_requested_key);
+        t->cached_requested_key = key_get(key);
+        set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
+#endif
+}
+
 /**
  * complete_request_key - Complete the construction of a key.
  * @authkey: The authorisation key.
@@ -218,7 +243,7 @@ static int construct_key(struct key *key, const void *callout_info,
         /* check that the actor called complete_request_key() prior to
          * returning an error */
         WARN_ON(ret < 0 &&
-                !test_bit(KEY_FLAG_REVOKED, &authkey->flags));
+                !test_bit(KEY_FLAG_INVALIDATED, &authkey->flags));
 
         key_put(authkey);
         kleave(" = %d", ret);
@@ -381,7 +406,9 @@ static int construct_alloc_key(struct keyring_search_context *ctx,
          * waited for locks */
         mutex_lock(&key_construction_mutex);
 
-        key_ref = search_process_keyrings(ctx);
+        rcu_read_lock();
+        key_ref = search_process_keyrings_rcu(ctx);
+        rcu_read_unlock();
         if (!IS_ERR(key_ref))
                 goto key_already_present;
 
@@ -556,10 +583,26 @@ struct key *request_key_and_link(struct key_type *type,
                 }
         }
 
+        key = check_cached_key(&ctx);
+        if (key)
+                return key;
+
         /* search all the process keyrings for a key */
-        key_ref = search_process_keyrings(&ctx);
+        rcu_read_lock();
+        key_ref = search_process_keyrings_rcu(&ctx);
+        rcu_read_unlock();
 
         if (!IS_ERR(key_ref)) {
+                if (dest_keyring) {
+                        ret = key_task_permission(key_ref, current_cred(),
+                                                  KEY_NEED_LINK);
+                        if (ret < 0) {
+                                key_ref_put(key_ref);
+                                key = ERR_PTR(ret);
+                                goto error_free;
+                        }
+                }
+
                 key = key_ref_to_ptr(key_ref);
                 if (dest_keyring) {
                         ret = key_link(dest_keyring, key);
@@ -569,6 +612,9 @@ struct key *request_key_and_link(struct key_type *type,
                                 goto error_free;
                         }
                 }
+
+                /* Only cache the key on immediate success */
+                cache_requested_key(key);
         } else if (PTR_ERR(key_ref) != -EAGAIN) {
                 key = ERR_CAST(key_ref);
         } else  {
@@ -689,52 +735,51 @@ struct key *request_key_with_auxdata(struct key_type *type,
 }
 EXPORT_SYMBOL(request_key_with_auxdata);
 
-/*
- * request_key_async - Request a key (allow async construction)
- * @type: Type of key.
- * @description: The searchable description of the key.
- * @callout_info: The data to pass to the instantiation upcall (or NULL).
- * @callout_len: The length of callout_info.
+/**
+ * request_key_rcu - Request key from RCU-read-locked context
+ * @type: The type of key we want.
+ * @description: The name of the key we want.
  *
- * As for request_key_and_link() except that it does not add the returned key
- * to a keyring if found, new keys are always allocated in the user's quota and
- * no auxiliary data can be passed.
+ * Request a key from a context that we may not sleep in (such as RCU-mode
+ * pathwalk).  Keys under construction are ignored.
  *
- * The caller should call wait_for_key_construction() to wait for the
- * completion of the returned key if it is still undergoing construction.
+ * Return a pointer to the found key if successful, -ENOKEY if we couldn't find
+ * a key or some other error if the key found was unsuitable or inaccessible.
  */
-struct key *request_key_async(struct key_type *type,
-                              const char *description,
-                              const void *callout_info,
-                              size_t callout_len)
+struct key *request_key_rcu(struct key_type *type, const char *description)
 {
-        return request_key_and_link(type, description, callout_info,
-                                    callout_len, NULL, NULL,
-                                    KEY_ALLOC_IN_QUOTA);
-}
-EXPORT_SYMBOL(request_key_async);
+        struct keyring_search_context ctx = {
+                .index_key.type         = type,
+                .index_key.description  = description,
+                .index_key.desc_len     = strlen(description),
+                .cred                   = current_cred(),
+                .match_data.cmp         = key_default_cmp,
+                .match_data.raw_data    = description,
+                .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
+                .flags                  = (KEYRING_SEARCH_DO_STATE_CHECK |
+                                           KEYRING_SEARCH_SKIP_EXPIRED),
+        };
+        struct key *key;
+        key_ref_t key_ref;
 
-/*
- * request a key with auxiliary data for the upcaller (allow async construction)
- * @type: Type of key.
- * @description: The searchable description of the key.
- * @callout_info: The data to pass to the instantiation upcall (or NULL).
- * @callout_len: The length of callout_info.
- * @aux: Auxiliary data for the upcall.
- *
- * As for request_key_and_link() except that it does not add the returned key
- * to a keyring if found and new keys are always allocated in the user's quota.
- *
- * The caller should call wait_for_key_construction() to wait for the
- * completion of the returned key if it is still undergoing construction.
- */
-struct key *request_key_async_with_auxdata(struct key_type *type,
-                                           const char *description,
-                                           const void *callout_info,
-                                           size_t callout_len,
-                                           void *aux)
-{
-        return request_key_and_link(type, description, callout_info,
-                                    callout_len, aux, NULL, KEY_ALLOC_IN_QUOTA);
+        kenter("%s,%s", type->name, description);
+
+        key = check_cached_key(&ctx);
+        if (key)
+                return key;
+
+        /* search all the process keyrings for a key */
+        key_ref = search_process_keyrings_rcu(&ctx);
+        if (IS_ERR(key_ref)) {
+                key = ERR_CAST(key_ref);
+                if (PTR_ERR(key_ref) == -EAGAIN)
+                        key = ERR_PTR(-ENOKEY);
+        } else {
+                key = key_ref_to_ptr(key_ref);
+                cache_requested_key(key);
+        }
+
+        kleave(" = %p", key);
+        return key;
 }
-EXPORT_SYMBOL(request_key_async_with_auxdata);
+EXPORT_SYMBOL(request_key_rcu);
diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index 3d8616f981b2..5456c0c72857 100644
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -54,7 +54,7 @@ static void request_key_auth_free_preparse(struct key_preparsed_payload *prep)
 static int request_key_auth_instantiate(struct key *key,
                                         struct key_preparsed_payload *prep)
 {
-        key->payload.data[0] = (struct request_key_auth *)prep->data;
+        rcu_assign_keypointer(key, (struct request_key_auth *)prep->data);
         return 0;
 }
 
@@ -64,7 +64,7 @@ static int request_key_auth_instantiate(struct key *key,
 static void request_key_auth_describe(const struct key *key,
                                       struct seq_file *m)
 {
-        struct request_key_auth *rka = get_request_key_auth(key);
+        struct request_key_auth *rka = dereference_key_rcu(key);
 
         seq_puts(m, "key:");
         seq_puts(m, key->description);
@@ -79,7 +79,7 @@ static void request_key_auth_describe(const struct key *key,
 static long request_key_auth_read(const struct key *key,
                                   char __user *buffer, size_t buflen)
 {
-        struct request_key_auth *rka = get_request_key_auth(key);
+        struct request_key_auth *rka = dereference_key_locked(key);
         size_t datalen;
         long ret;
 
@@ -98,23 +98,6 @@ static long request_key_auth_read(const struct key *key,
         return ret;
 }
 
-/*
- * Handle revocation of an authorisation token key.
- *
- * Called with the key sem write-locked.
- */
-static void request_key_auth_revoke(struct key *key)
-{
-        struct request_key_auth *rka = get_request_key_auth(key);
-
-        kenter("{%d}", key->serial);
-
-        if (rka->cred) {
-                put_cred(rka->cred);
-                rka->cred = NULL;
-        }
-}
-
 static void free_request_key_auth(struct request_key_auth *rka)
 {
         if (!rka)
@@ -128,15 +111,42 @@ static void free_request_key_auth(struct request_key_auth *rka)
 }
 
 /*
+ * Dispose of the request_key_auth record under RCU conditions
+ */
+static void request_key_auth_rcu_disposal(struct rcu_head *rcu)
+{
+        struct request_key_auth *rka =
+                container_of(rcu, struct request_key_auth, rcu);
+
+        free_request_key_auth(rka);
+}
+
+/*
+ * Handle revocation of an authorisation token key.
+ *
+ * Called with the key sem write-locked.
+ */
+static void request_key_auth_revoke(struct key *key)
+{
+        struct request_key_auth *rka = dereference_key_locked(key);
+
+        kenter("{%d}", key->serial);
+        rcu_assign_keypointer(key, NULL);
+        call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
+}
+
+/*
  * Destroy an instantiation authorisation token key.
  */
 static void request_key_auth_destroy(struct key *key)
 {
-        struct request_key_auth *rka = get_request_key_auth(key);
+        struct request_key_auth *rka = rcu_access_pointer(key->payload.rcu_data0);
 
         kenter("{%d}", key->serial);
-
-        free_request_key_auth(rka);
+        if (rka) {
+                rcu_assign_keypointer(key, NULL);
+                call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
+        }
 }
 
 /*
@@ -245,7 +255,9 @@ struct key *key_get_instantiation_authkey(key_serial_t target_id)
 
         ctx.index_key.desc_len = sprintf(description, "%x", target_id);
 
-        authkey_ref = search_process_keyrings(&ctx);
+        rcu_read_lock();
+        authkey_ref = search_process_keyrings_rcu(&ctx);
+        rcu_read_unlock();
 
         if (IS_ERR(authkey_ref)) {
                 authkey = ERR_CAST(authkey_ref);