KEYS: Do preallocation for __key_link()

Do preallocation for __key_link() so that the various callers in request_key.c
can deal with any errors from this source before attempting to construct a key.
This allows them to assume that the actual linkage step is guaranteed to be
successful.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

4 files changed, 215 insertions, 130 deletions

diff --git a/security/keys/internal.h b/security/keys/internal.h
index 24ba0307b7ad..5d4402a1161a 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -87,7 +87,16 @@ extern wait_queue_head_t request_key_conswq;
 extern struct key_type *key_type_lookup(const char *type);
 extern void key_type_put(struct key_type *ktype);
 
-extern int __key_link(struct key *keyring, struct key *key);
+extern int __key_link_begin(struct key *keyring,
+                            const struct key_type *type,
+                            const char *description,
+                            struct keyring_list **_prealloc);
+extern int __key_link_check_live_key(struct key *keyring, struct key *key);
+extern void __key_link(struct key *keyring, struct key *key,
+                       struct keyring_list **_prealloc);
+extern void __key_link_end(struct key *keyring,
+                           struct key_type *type,
+                           struct keyring_list *prealloc);
 
 extern key_ref_t __keyring_search_one(key_ref_t keyring_ref,
                                       const struct key_type *type,
diff --git a/security/keys/key.c b/security/keys/key.c
index c70da6fb82ce..c1eac8084ade 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -398,7 +398,8 @@ static int __key_instantiate_and_link(struct key *key,
                                       const void *data,
                                       size_t datalen,
                                       struct key *keyring,
-                                      struct key *authkey)
+                                      struct key *authkey,
+                                      struct keyring_list **_prealloc)
 {
         int ret, awaken;
 
@@ -425,7 +426,7 @@ static int __key_instantiate_and_link(struct key *key,
 
                         /* and link it into the destination keyring */
                         if (keyring)
-                                ret = __key_link(keyring, key);
+                                __key_link(keyring, key, _prealloc);
 
                         /* disable the authorisation key */
                         if (authkey)
@@ -453,15 +454,21 @@ int key_instantiate_and_link(struct key *key,
                              struct key *keyring,
                              struct key *authkey)
 {
+        struct keyring_list *prealloc;
         int ret;
 
-        if (keyring)
-                down_write(&keyring->sem);
+        if (keyring) {
+                ret = __key_link_begin(keyring, key->type, key->description,
+                                       &prealloc);
+                if (ret < 0)
+                        return ret;
+        }
 
-        ret = __key_instantiate_and_link(key, data, datalen, keyring, authkey);
+        ret = __key_instantiate_and_link(key, data, datalen, keyring, authkey,
+                                         &prealloc);
 
         if (keyring)
-                up_write(&keyring->sem);
+                __key_link_end(keyring, key->type, prealloc);
 
         return ret;
 
@@ -478,8 +485,9 @@ int key_negate_and_link(struct key *key,
                         struct key *keyring,
                         struct key *authkey)
 {
+        struct keyring_list *prealloc;
         struct timespec now;
-        int ret, awaken;
+        int ret, awaken, link_ret = 0;
 
         key_check(key);
         key_check(keyring);
@@ -488,7 +496,8 @@ int key_negate_and_link(struct key *key,
         ret = -EBUSY;
 
         if (keyring)
-                down_write(&keyring->sem);
+                link_ret = __key_link_begin(keyring, key->type,
+                                            key->description, &prealloc);
 
         mutex_lock(&key_construction_mutex);
 
@@ -508,8 +517,8 @@ int key_negate_and_link(struct key *key,
                 ret = 0;
 
                 /* and link it into the destination keyring */
-                if (keyring)
-                        ret = __key_link(keyring, key);
+                if (keyring && link_ret == 0)
+                        __key_link(keyring, key, &prealloc);
 
                 /* disable the authorisation key */
                 if (authkey)
@@ -519,13 +528,13 @@ int key_negate_and_link(struct key *key,
         mutex_unlock(&key_construction_mutex);
 
         if (keyring)
-                up_write(&keyring->sem);
+                __key_link_end(keyring, key->type, prealloc);
 
         /* wake up anyone waiting for a key to be constructed */
         if (awaken)
                 wake_up_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT);
 
-        return ret;
+        return ret == 0 ? link_ret : ret;
 
 } /* end key_negate_and_link() */
 
@@ -749,6 +758,7 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
                                key_perm_t perm,
                                unsigned long flags)
 {
+        struct keyring_list *prealloc;
         const struct cred *cred = current_cred();
         struct key_type *ktype;
         struct key *keyring, *key = NULL;
@@ -775,7 +785,9 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
         if (keyring->type != &key_type_keyring)
                 goto error_2;
 
-        down_write(&keyring->sem);
+        ret = __key_link_begin(keyring, ktype, description, &prealloc);
+        if (ret < 0)
+                goto error_2;
 
         /* if we're going to allocate a new key, we're going to have
          * to modify the keyring */
@@ -817,7 +829,8 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
         }
 
         /* instantiate it and link it into the target keyring */
-        ret = __key_instantiate_and_link(key, payload, plen, keyring, NULL);
+        ret = __key_instantiate_and_link(key, payload, plen, keyring, NULL,
+                                         &prealloc);
         if (ret < 0) {
                 key_put(key);
                 key_ref = ERR_PTR(ret);
@@ -827,7 +840,7 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
         key_ref = make_key_ref(key, is_key_possessed(keyring_ref));
 
  error_3:
-        up_write(&keyring->sem);
+        __key_link_end(keyring, ktype, prealloc);
  error_2:
         key_type_put(ktype);
  error:
@@ -837,7 +850,7 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
         /* we found a matching key, so we're going to try to update it
          * - we can drop the locks first as we have the key pinned
          */
-        up_write(&keyring->sem);
+        __key_link_end(keyring, ktype, prealloc);
         key_type_put(ktype);
 
         key_ref = __key_update(key_ref, payload, plen);
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 3f425a65906f..ef03a82a0135 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -660,20 +660,6 @@ cycle_detected:
 
 } /* end keyring_detect_cycle() */
 
-/*****************************************************************************/
-/*
- * dispose of a keyring list after the RCU grace period
- */
-static void keyring_link_rcu_disposal(struct rcu_head *rcu)
-{
-        struct keyring_list *klist =
-                container_of(rcu, struct keyring_list, rcu);
-
-        kfree(klist);
-
-} /* end keyring_link_rcu_disposal() */
-
-/*****************************************************************************/
 /*
  * dispose of a keyring list after the RCU grace period, freeing the unlinked
  * key
@@ -683,56 +669,51 @@ static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
         struct keyring_list *klist =
                 container_of(rcu, struct keyring_list, rcu);
 
-        key_put(klist->keys[klist->delkey]);
+        if (klist->delkey != USHORT_MAX)
+                key_put(klist->keys[klist->delkey]);
         kfree(klist);
+}
 
-} /* end keyring_unlink_rcu_disposal() */
-
-/*****************************************************************************/
 /*
- * link a key into to a keyring
- * - must be called with the keyring's semaphore write-locked
- * - discard already extant link to matching key if there is one
+ * preallocate memory so that a key can be linked into to a keyring
  */
-int __key_link(struct key *keyring, struct key *key)
+int __key_link_begin(struct key *keyring, const struct key_type *type,
+                     const char *description,
+                     struct keyring_list **_prealloc)
+        __acquires(&keyring->sem)
 {
         struct keyring_list *klist, *nklist;
         unsigned max;
         size_t size;
         int loop, ret;
 
-        ret = -EKEYREVOKED;
-        if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
-                goto error;
+        kenter("%d,%s,%s,", key_serial(keyring), type->name, description);
 
-        ret = -ENOTDIR;
         if (keyring->type != &key_type_keyring)
-                goto error;
+                return -ENOTDIR;
+
+        down_write(&keyring->sem);
+
+        ret = -EKEYREVOKED;
+        if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
+                goto error_krsem;
 
-        /* do some special keyring->keyring link checks */
-        if (key->type == &key_type_keyring) {
-                /* serialise link/link calls to prevent parallel calls causing
-                 * a cycle when applied to two keyring in opposite orders */
+        /* serialise link/link calls to prevent parallel calls causing a cycle
+         * when linking two keyring in opposite orders */
+        if (type == &key_type_keyring)
                 down_write(&keyring_serialise_link_sem);
 
-                /* check that we aren't going to create a cycle adding one
-                 * keyring to another */
-                ret = keyring_detect_cycle(keyring, key);
-                if (ret < 0)
-                        goto error2;
-        }
+        klist = rcu_dereference_locked_keyring(keyring);
 
         /* see if there's a matching key we can displace */
-        klist = rcu_dereference_locked_keyring(keyring);
         if (klist && klist->nkeys > 0) {
-                struct key_type *type = key->type;
-
                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
                         if (klist->keys[loop]->type == type &&
                             strcmp(klist->keys[loop]->description,
-                                   key->description) == 0
+                                   description) == 0
                             ) {
-                                /* found a match - replace with new key */
+                                /* found a match - we'll replace this one with
+                                 * the new key */
                                 size = sizeof(struct key *) * klist->maxkeys;
                                 size += sizeof(*klist);
                                 BUG_ON(size > PAGE_SIZE);
@@ -740,22 +721,10 @@ int __key_link(struct key *keyring, struct key *key)
                                 ret = -ENOMEM;
                                 nklist = kmemdup(klist, size, GFP_KERNEL);
                                 if (!nklist)
-                                        goto error2;
-
-                                /* replace matched key */
-                                atomic_inc(&key->usage);
-                                nklist->keys[loop] = key;
-
-                                rcu_assign_pointer(
-                                        keyring->payload.subscriptions,
-                                        nklist);
-
-                                /* dispose of the old keyring list and the
-                                 * displaced key */
-                                klist->delkey = loop;
-                                call_rcu(&klist->rcu,
-                                         keyring_unlink_rcu_disposal);
+                                        goto error_sem;
 
+                                /* note replacement slot */
+                                klist->delkey = nklist->delkey = loop;
                                 goto done;
                         }
                 }
@@ -765,16 +734,11 @@ int __key_link(struct key *keyring, struct key *key)
         ret = key_payload_reserve(keyring,
                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
         if (ret < 0)
-                goto error2;
+                goto error_sem;
 
         if (klist && klist->nkeys < klist->maxkeys) {
-                /* there's sufficient slack space to add directly */
-                atomic_inc(&key->usage);
-
-                klist->keys[klist->nkeys] = key;
-                smp_wmb();
-                klist->nkeys++;
-                smp_wmb();
+                /* there's sufficient slack space to append directly */
+                nklist = NULL;
         } else {
                 /* grow the key list */
                 max = 4;
@@ -782,71 +746,155 @@ int __key_link(struct key *keyring, struct key *key)
                         max += klist->maxkeys;
 
                 ret = -ENFILE;
-                if (max > 65535)
-                        goto error3;
+                if (max > USHORT_MAX - 1)
+                        goto error_quota;
                 size = sizeof(*klist) + sizeof(struct key *) * max;
                 if (size > PAGE_SIZE)
-                        goto error3;
+                        goto error_quota;
 
                 ret = -ENOMEM;
                 nklist = kmalloc(size, GFP_KERNEL);
                 if (!nklist)
-                        goto error3;
-                nklist->maxkeys = max;
-                nklist->nkeys = 0;
+                        goto error_quota;
 
+                nklist->maxkeys = max;
                 if (klist) {
-                        nklist->nkeys = klist->nkeys;
-                        memcpy(nklist->keys,
-                               klist->keys,
+                        memcpy(nklist->keys, klist->keys,
                                sizeof(struct key *) * klist->nkeys);
+                        nklist->delkey = klist->nkeys;
+                        nklist->nkeys = klist->nkeys + 1;
+                        klist->delkey = USHORT_MAX;
+                } else {
+                        nklist->nkeys = 1;
+                        nklist->delkey = 0;
                 }
 
                 /* add the key into the new space */
-                atomic_inc(&key->usage);
-                nklist->keys[nklist->nkeys++] = key;
-
-                rcu_assign_pointer(keyring->payload.subscriptions, nklist);
-
-                /* dispose of the old keyring list */
-                if (klist)
-                        call_rcu(&klist->rcu, keyring_link_rcu_disposal);
+                nklist->keys[nklist->delkey] = NULL;
         }
 
 done:
-        ret = 0;
-error2:
-        if (key->type == &key_type_keyring)
-                up_write(&keyring_serialise_link_sem);
-error:
-        return ret;
+        *_prealloc = nklist;
+        kleave(" = 0");
+        return 0;
 
-error3:
+error_quota:
         /* undo the quota changes */
         key_payload_reserve(keyring,
                             keyring->datalen - KEYQUOTA_LINK_BYTES);
-        goto error2;
+error_sem:
+        if (type == &key_type_keyring)
+                up_write(&keyring_serialise_link_sem);
+error_krsem:
+        up_write(&keyring->sem);
+        kleave(" = %d", ret);
+        return ret;
+}
 
-} /* end __key_link() */
+/*
+ * check already instantiated keys aren't going to be a problem
+ * - the caller must have called __key_link_begin()
+ * - don't need to call this for keys that were created since __key_link_begin()
+ *   was called
+ */
+int __key_link_check_live_key(struct key *keyring, struct key *key)
+{
+        if (key->type == &key_type_keyring)
+                /* check that we aren't going to create a cycle by linking one
+                 * keyring to another */
+                return keyring_detect_cycle(keyring, key);
+        return 0;
+}
+
+/*
+ * link a key into to a keyring
+ * - must be called with __key_link_begin() having being called
+ * - discard already extant link to matching key if there is one
+ */
+void __key_link(struct key *keyring, struct key *key,
+                struct keyring_list **_prealloc)
+{
+        struct keyring_list *klist, *nklist;
+
+        nklist = *_prealloc;
+        *_prealloc = NULL;
+
+        kenter("%d,%d,%p", keyring->serial, key->serial, nklist);
+
+        klist = rcu_dereference_protected(keyring->payload.subscriptions,
+                                          rwsem_is_locked(&keyring->sem));
+
+        atomic_inc(&key->usage);
+
+        /* there's a matching key we can displace or an empty slot in a newly
+         * allocated list we can fill */
+        if (nklist) {
+                kdebug("replace %hu/%hu/%hu",
+                       nklist->delkey, nklist->nkeys, nklist->maxkeys);
+
+                nklist->keys[nklist->delkey] = key;
+
+                rcu_assign_pointer(keyring->payload.subscriptions, nklist);
+
+                /* dispose of the old keyring list and, if there was one, the
+                 * displaced key */
+                if (klist) {
+                        kdebug("dispose %hu/%hu/%hu",
+                               klist->delkey, klist->nkeys, klist->maxkeys);
+                        call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
+                }
+        } else {
+                /* there's sufficient slack space to append directly */
+                klist->keys[klist->nkeys] = key;
+                smp_wmb();
+                klist->nkeys++;
+        }
+}
+
+/*
+ * finish linking a key into to a keyring
+ * - must be called with __key_link_begin() having being called
+ */
+void __key_link_end(struct key *keyring, struct key_type *type,
+                    struct keyring_list *prealloc)
+        __releases(&keyring->sem)
+{
+        BUG_ON(type == NULL);
+        BUG_ON(type->name == NULL);
+        kenter("%d,%s,%p", keyring->serial, type->name, prealloc);
+
+        if (type == &key_type_keyring)
+                up_write(&keyring_serialise_link_sem);
+
+        if (prealloc) {
+                kfree(prealloc);
+                key_payload_reserve(keyring,
+                                    keyring->datalen - KEYQUOTA_LINK_BYTES);
+        }
+        up_write(&keyring->sem);
+}
 
-/*****************************************************************************/
 /*
  * link a key to a keyring
  */
 int key_link(struct key *keyring, struct key *key)
 {
+        struct keyring_list *prealloc;
         int ret;
 
         key_check(keyring);
         key_check(key);
 
-        down_write(&keyring->sem);
-        ret = __key_link(keyring, key);
-        up_write(&keyring->sem);
+        ret = __key_link_begin(keyring, key->type, key->description, &prealloc);
+        if (ret == 0) {
+                ret = __key_link_check_live_key(keyring, key);
+                if (ret == 0)
+                        __key_link(keyring, key, &prealloc);
+                __key_link_end(keyring, key->type, prealloc);
+        }
 
         return ret;
-
-} /* end key_link() */
+}
 
 EXPORT_SYMBOL(key_link);
 
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index ac49c8aacbf0..f656e9c069e3 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -299,6 +299,7 @@ static int construct_alloc_key(struct key_type *type,
                                struct key_user *user,
                                struct key **_key)
 {
+        struct keyring_list *prealloc;
         const struct cred *cred = current_cred();
         struct key *key;
         key_ref_t key_ref;
@@ -306,6 +307,7 @@ static int construct_alloc_key(struct key_type *type,
 
         kenter("%s,%s,,,", type->name, description);
 
+        *_key = NULL;
         mutex_lock(&user->cons_lock);
 
         key = key_alloc(type, description, cred->fsuid, cred->fsgid, cred,
@@ -315,8 +317,12 @@ static int construct_alloc_key(struct key_type *type,
 
         set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
 
-        if (dest_keyring)
-                down_write(&dest_keyring->sem);
+        if (dest_keyring) {
+                ret = __key_link_begin(dest_keyring, type, description,
+                                       &prealloc);
+                if (ret < 0)
+                        goto link_prealloc_failed;
+        }
 
         /* attach the key to the destination keyring under lock, but we do need
          * to do another check just in case someone beat us to it whilst we
@@ -328,11 +334,11 @@ static int construct_alloc_key(struct key_type *type,
                 goto key_already_present;
 
         if (dest_keyring)
-                __key_link(dest_keyring, key);
+                __key_link(dest_keyring, key, &prealloc);
 
         mutex_unlock(&key_construction_mutex);
         if (dest_keyring)
-                up_write(&dest_keyring->sem);
+                __key_link_end(dest_keyring, type, prealloc);
         mutex_unlock(&user->cons_lock);
         *_key = key;
         kleave(" = 0 [%d]", key_serial(key));
@@ -341,27 +347,36 @@ static int construct_alloc_key(struct key_type *type,
         /* the key is now present - we tell the caller that we found it by
          * returning -EINPROGRESS  */
 key_already_present:
+        key_put(key);
         mutex_unlock(&key_construction_mutex);
-        ret = 0;
+        key = key_ref_to_ptr(key_ref);
         if (dest_keyring) {
-                ret = __key_link(dest_keyring, key_ref_to_ptr(key_ref));
-                up_write(&dest_keyring->sem);
+                ret = __key_link_check_live_key(dest_keyring, key);
+                if (ret == 0)
+                        __key_link(dest_keyring, key, &prealloc);
+                __key_link_end(dest_keyring, type, prealloc);
+                if (ret < 0)
+                        goto link_check_failed;
         }
         mutex_unlock(&user->cons_lock);
-        key_put(key);
-        if (ret < 0) {
-                key_ref_put(key_ref);
-                *_key = NULL;
-                kleave(" = %d [link]", ret);
-                return ret;
-        }
-        *_key = key = key_ref_to_ptr(key_ref);
+        *_key = key;
         kleave(" = -EINPROGRESS [%d]", key_serial(key));
         return -EINPROGRESS;
 
+link_check_failed:
+        mutex_unlock(&user->cons_lock);
+        key_put(key);
+        kleave(" = %d [linkcheck]", ret);
+        return ret;
+
+link_prealloc_failed:
+        up_write(&dest_keyring->sem);
+        mutex_unlock(&user->cons_lock);
+        kleave(" = %d [prelink]", ret);
+        return ret;
+
 alloc_failed:
         mutex_unlock(&user->cons_lock);
-        *_key = NULL;
         kleave(" = %ld", PTR_ERR(key));
         return PTR_ERR(key);
 }