KEYS: Fix __key_link_end() quota fixup on error

Fix __key_link_end()'s attempt to fix up the quota if an error occurs.

There are two erroneous cases: Firstly, we always decrease the quota if
the preallocated replacement keyring needs cleaning up, irrespective of
whether or not we should (we may have replaced a pointer rather than
adding another pointer).

Secondly, we never clean up the quota if we added a pointer without the
keyring storage being extended (we allocate multiple pointers at a time,
even if we're not going to use them all immediately).

We handle this by setting the bottom bit of the preallocation pointer in
__key_link_begin() to indicate that the quota needs fixing up, which is
then passed to __key_link() (which clears the whole thing) and
__key_link_end().

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 27 insertions, 20 deletions

diff --git a/security/keys/internal.h b/security/keys/internal.h
index edfa50dbd6f5..a52aa7c88b41 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -87,13 +87,13 @@ extern void key_type_put(struct key_type *ktype);
 extern int __key_link_begin(struct key *keyring,
                             const struct key_type *type,
                             const char *description,
-                            struct keyring_list **_prealloc);
+                            unsigned long *_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);
+                       unsigned long *_prealloc);
 extern void __key_link_end(struct key *keyring,
                            struct key_type *type,
-                           struct keyring_list *prealloc);
+                           unsigned long 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 84d4eb568b08..1c2d43dc5107 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -415,7 +415,7 @@ static int __key_instantiate_and_link(struct key *key,
                                       size_t datalen,
                                       struct key *keyring,
                                       struct key *authkey,
-                                      struct keyring_list **_prealloc)
+                                      unsigned long *_prealloc)
 {
         int ret, awaken;
 
@@ -481,7 +481,7 @@ int key_instantiate_and_link(struct key *key,
                              struct key *keyring,
                              struct key *authkey)
 {
-        struct keyring_list *prealloc;
+        unsigned long prealloc;
         int ret;
 
         if (keyring) {
@@ -526,7 +526,7 @@ int key_negate_and_link(struct key *key,
                         struct key *keyring,
                         struct key *authkey)
 {
-        struct keyring_list *prealloc;
+        unsigned long prealloc;
         struct timespec now;
         int ret, awaken, link_ret = 0;
 
@@ -814,7 +814,7 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
                                key_perm_t perm,
                                unsigned long flags)
 {
-        struct keyring_list *prealloc;
+        unsigned long prealloc;
         const struct cred *cred = current_cred();
         struct key_type *ktype;
         struct key *keyring, *key = NULL;
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 92024ed12e0a..5620f084dede 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -25,6 +25,8 @@
                 (keyring)->payload.subscriptions,                       \
                 rwsem_is_locked((struct rw_semaphore *)&(keyring)->sem)))
 
+#define KEY_LINK_FIXQUOTA 1UL
+
 /*
  * When plumbing the depths of the key tree, this sets a hard limit
  * set on how deep we're willing to go.
@@ -699,11 +701,11 @@ static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
  * Preallocate memory so that a key can be linked into to a keyring.
  */
 int __key_link_begin(struct key *keyring, const struct key_type *type,
-                     const char *description,
-                     struct keyring_list **_prealloc)
+                     const char *description, unsigned long *_prealloc)
         __acquires(&keyring->sem)
 {
         struct keyring_list *klist, *nklist;
+        unsigned long prealloc;
         unsigned max;
         size_t size;
         int loop, ret;
@@ -746,6 +748,7 @@ int __key_link_begin(struct key *keyring, const struct key_type *type,
 
                                 /* note replacement slot */
                                 klist->delkey = nklist->delkey = loop;
+                                prealloc = (unsigned long)nklist;
                                 goto done;
                         }
                 }
@@ -760,6 +763,7 @@ int __key_link_begin(struct key *keyring, const struct key_type *type,
         if (klist && klist->nkeys < klist->maxkeys) {
                 /* there's sufficient slack space to append directly */
                 nklist = NULL;
+                prealloc = KEY_LINK_FIXQUOTA;
         } else {
                 /* grow the key list */
                 max = 4;
@@ -794,8 +798,9 @@ int __key_link_begin(struct key *keyring, const struct key_type *type,
                 nklist->keys[nklist->delkey] = NULL;
         }
 
+        prealloc = (unsigned long)nklist | KEY_LINK_FIXQUOTA;
 done:
-        *_prealloc = nklist;
+        *_prealloc = prealloc;
         kleave(" = 0");
         return 0;
 
@@ -836,12 +841,12 @@ int __key_link_check_live_key(struct key *keyring, struct key *key)
  * combination.
  */
 void __key_link(struct key *keyring, struct key *key,
-                struct keyring_list **_prealloc)
+                unsigned long *_prealloc)
 {
         struct keyring_list *klist, *nklist;
 
-        nklist = *_prealloc;
-        *_prealloc = NULL;
+        nklist = (struct keyring_list *)(*_prealloc & ~KEY_LINK_FIXQUOTA);
+        *_prealloc = 0;
 
         kenter("%d,%d,%p", keyring->serial, key->serial, nklist);
 
@@ -881,20 +886,22 @@ void __key_link(struct key *keyring, struct key *key,
  * 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)
+                    unsigned long prealloc)
         __releases(&keyring->sem)
 {
         BUG_ON(type == NULL);
         BUG_ON(type->name == NULL);
-        kenter("%d,%s,%p", keyring->serial, type->name, prealloc);
+        kenter("%d,%s,%lx", 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);
+                if (prealloc & KEY_LINK_FIXQUOTA)
+                        key_payload_reserve(keyring,
+                                            keyring->datalen -
+                                            KEYQUOTA_LINK_BYTES);
+                kfree((struct keyring_list *)(prealloc & ~KEY_LINK_FIXQUOTA));
         }
         up_write(&keyring->sem);
 }
@@ -921,7 +928,7 @@ void __key_link_end(struct key *keyring, struct key_type *type,
  */
 int key_link(struct key *keyring, struct key *key)
 {
-        struct keyring_list *prealloc;
+        unsigned long prealloc;
         int ret;
 
         key_check(keyring);
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 9a7fb3914b27..a3dc0d460def 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -352,8 +352,8 @@ 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();
+        unsigned long prealloc;
         struct key *key;
         key_ref_t key_ref;
         int ret;