cred: add get_cred_many and put_cred_many

Some of the frequent consumers of get_cred and put_cred operate on 2
references on the same creds back-to-back.

Switch them to doing the work in one go instead.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
[PM: removed changelog from commit description]
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/include/linux/cred.h b/include/linux/cred.h
index f923528d5cc43aaee8e7573844f4843ae295e110..56bc432fe49bf1612120f1b1d0f7acb3a9f9992f 100644 (file)
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -218,6 +218,20 @@ static inline bool cap_ambient_invariant_ok(const struct cred *cred)
                                          cred->cap_inheritable));
 }
 
+/**
+ * get_new_cred_many - Get references on a new set of credentials
+ * @cred: The new credentials to reference
+ * @nr: Number of references to acquire
+ *
+ * Get references on the specified set of new credentials.  The caller must
+ * release all acquired references.
+ */
+static inline struct cred *get_new_cred_many(struct cred *cred, int nr)
+{
+       atomic_add(nr, &cred->usage);
+       return cred;
+}
+
 /**
  * get_new_cred - Get a reference on a new set of credentials
  * @cred: The new credentials to reference
@@ -227,16 +241,16 @@ static inline bool cap_ambient_invariant_ok(const struct cred *cred)
  */
 static inline struct cred *get_new_cred(struct cred *cred)
 {
-       atomic_inc(&cred->usage);
-       return cred;
+       return get_new_cred_many(cred, 1);
 }
 
 /**
- * get_cred - Get a reference on a set of credentials
+ * get_cred_many - Get references on a set of credentials
  * @cred: The credentials to reference
+ * @nr: Number of references to acquire
  *
- * Get a reference on the specified set of credentials.  The caller must
- * release the reference.  If %NULL is passed, it is returned with no action.
+ * Get references on the specified set of credentials.  The caller must release
+ * all acquired reference.  If %NULL is passed, it is returned with no action.
  *
  * This is used to deal with a committed set of credentials.  Although the
  * pointer is const, this will temporarily discard the const and increment the
@@ -244,14 +258,28 @@ static inline struct cred *get_new_cred(struct cred *cred)
  * accidental alteration of a set of credentials that should be considered
  * immutable.
  */
-static inline const struct cred *get_cred(const struct cred *cred)
+static inline const struct cred *get_cred_many(const struct cred *cred, int nr)
 {
        struct cred *nonconst_cred = (struct cred *) cred;
        if (!cred)
                return cred;
        validate_creds(cred);
        nonconst_cred->non_rcu = 0;
-       return get_new_cred(nonconst_cred);
+       return get_new_cred_many(nonconst_cred, nr);
+}
+
+/*
+ * get_cred - Get a reference on a set of credentials
+ * @cred: The credentials to reference
+ *
+ * Get a reference on the specified set of credentials.  The caller must
+ * release the reference.  If %NULL is passed, it is returned with no action.
+ *
+ * This is used to deal with a committed set of credentials.
+ */
+static inline const struct cred *get_cred(const struct cred *cred)
+{
+       return get_cred_many(cred, 1);
 }
 
 static inline const struct cred *get_cred_rcu(const struct cred *cred)
@@ -269,6 +297,7 @@ static inline const struct cred *get_cred_rcu(const struct cred *cred)
 /**
  * put_cred - Release a reference to a set of credentials
  * @cred: The credentials to release
+ * @nr: Number of references to release
  *
  * Release a reference to a set of credentials, deleting them when the last ref
  * is released.  If %NULL is passed, nothing is done.
@@ -277,17 +306,29 @@ static inline const struct cred *get_cred_rcu(const struct cred *cred)
  * on task_struct are attached by const pointers to prevent accidental
  * alteration of otherwise immutable credential sets.
  */
-static inline void put_cred(const struct cred *_cred)
+static inline void put_cred_many(const struct cred *_cred, int nr)
 {
        struct cred *cred = (struct cred *) _cred;
 
        if (cred) {
                validate_creds(cred);
-               if (atomic_dec_and_test(&(cred)->usage))
+               if (atomic_sub_and_test(nr, &cred->usage))
                        __put_cred(cred);
        }
 }
 
+/*
+ * put_cred - Release a reference to a set of credentials
+ * @cred: The credentials to release
+ *
+ * Release a reference to a set of credentials, deleting them when the last ref
+ * is released.  If %NULL is passed, nothing is done.
+ */
+static inline void put_cred(const struct cred *cred)
+{
+       put_cred_many(cred, 1);
+}
+
 /**
  * current_cred - Access the current task's subjective credentials
  *

diff --git a/kernel/cred.c b/kernel/cred.c
index 98cb4eca23fb2fb2722b9e5d00d4a3f8ab51fd23..9398e534b997b8370012bfac7ff3893bba0f102a 100644 (file)
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -162,23 +162,29 @@ EXPORT_SYMBOL(__put_cred);
  */
 void exit_creds(struct task_struct *tsk)
 {
-       struct cred *cred;
+       struct cred *real_cred, *cred;
 
        kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
               atomic_read(&tsk->cred->usage),
               read_cred_subscribers(tsk->cred));
 
-       cred = (struct cred *) tsk->real_cred;
+       real_cred = (struct cred *) tsk->real_cred;
        tsk->real_cred = NULL;
-       validate_creds(cred);
-       alter_cred_subscribers(cred, -1);
-       put_cred(cred);
 
        cred = (struct cred *) tsk->cred;
        tsk->cred = NULL;
+
        validate_creds(cred);
-       alter_cred_subscribers(cred, -1);
-       put_cred(cred);
+       if (real_cred == cred) {
+               alter_cred_subscribers(cred, -2);
+               put_cred_many(cred, 2);
+       } else {
+               validate_creds(real_cred);
+               alter_cred_subscribers(real_cred, -1);
+               put_cred(real_cred);
+               alter_cred_subscribers(cred, -1);
+               put_cred(cred);
+       }
 
 #ifdef CONFIG_KEYS_REQUEST_CACHE
        key_put(tsk->cached_requested_key);
@@ -355,8 +361,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
 #endif
                clone_flags & CLONE_THREAD
            ) {
-               p->real_cred = get_cred(p->cred);
-               get_cred(p->cred);
+               p->real_cred = get_cred_many(p->cred, 2);
                alter_cred_subscribers(p->cred, 2);
                kdebug("share_creds(%p{%d,%d})",
                       p->cred, atomic_read(&p->cred->usage),
@@ -520,8 +525,7 @@ int commit_creds(struct cred *new)
                proc_id_connector(task, PROC_EVENT_GID);
 
        /* release the old obj and subj refs both */
-       put_cred(old);
-       put_cred(old);
+       put_cred_many(old, 2);
        return 0;
 }
 EXPORT_SYMBOL(commit_creds);