CRED: Wrap current->cred and a few other accessors

Wrap current->cred and a few other accessors to hide their actual
implementation.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 143 insertions, 44 deletions

diff --git a/include/linux/cred.h b/include/linux/cred.h
index a7a686074cb0..4221ec6000c1 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -37,15 +37,16 @@ struct group_info {
  * get_group_info - Get a reference to a group info structure
  * @group_info: The group info to reference
  *
- * This must be called with the owning task locked (via task_lock()) when task
- * != current.  The reason being that the vast majority of callers are looking
- * at current->group_info, which can not be changed except by the current task.
- * Changing current->group_info requires the task lock, too.
+ * This gets a reference to a set of supplementary groups.
+ *
+ * If the caller is accessing a task's credentials, they must hold the RCU read
+ * lock when reading.
  */
-#define get_group_info(group_info)              \
-do {                                            \
-        atomic_inc(&(group_info)->usage);       \
-} while (0)
+static inline struct group_info *get_group_info(struct group_info *gi)
+{
+        atomic_inc(&gi->usage);
+        return gi;
+}
 
 /**
  * put_group_info - Release a reference to a group info structure
@@ -61,7 +62,7 @@ extern struct group_info *groups_alloc(int);
 extern void groups_free(struct group_info *);
 extern int set_current_groups(struct group_info *);
 extern int set_groups(struct cred *, struct group_info *);
-extern int groups_search(struct group_info *, gid_t);
+extern int groups_search(const struct group_info *, gid_t);
 
 /* access the groups "array" with this macro */
 #define GROUP_AT(gi, i) \
@@ -123,41 +124,6 @@ struct cred {
         spinlock_t      lock;           /* lock for pointer changes */
 };
 
-#define get_current_user()      (get_uid(current->cred->user))
-
-#define task_uid(task)          ((task)->cred->uid)
-#define task_gid(task)          ((task)->cred->gid)
-#define task_euid(task)         ((task)->cred->euid)
-#define task_egid(task)         ((task)->cred->egid)
-
-#define current_uid()           (current->cred->uid)
-#define current_gid()           (current->cred->gid)
-#define current_euid()          (current->cred->euid)
-#define current_egid()          (current->cred->egid)
-#define current_suid()          (current->cred->suid)
-#define current_sgid()          (current->cred->sgid)
-#define current_fsuid()         (current->cred->fsuid)
-#define current_fsgid()         (current->cred->fsgid)
-#define current_cap()           (current->cred->cap_effective)
-
-#define current_uid_gid(_uid, _gid)             \
-do {                                            \
-        *(_uid) = current->cred->uid;           \
-        *(_gid) = current->cred->gid;           \
-} while(0)
-
-#define current_euid_egid(_uid, _gid)           \
-do {                                            \
-        *(_uid) = current->cred->euid;          \
-        *(_gid) = current->cred->egid;          \
-} while(0)
-
-#define current_fsuid_fsgid(_uid, _gid)         \
-do {                                            \
-        *(_uid) = current->cred->fsuid;         \
-        *(_gid) = current->cred->fsgid;         \
-} while(0)
-
 extern void __put_cred(struct cred *);
 extern int copy_creds(struct task_struct *, unsigned long);
 
@@ -187,4 +153,137 @@ static inline void put_cred(struct cred *cred)
                 __put_cred(cred);
 }
 
+/**
+ * current_cred - Access the current task's credentials
+ *
+ * Access the credentials of the current task.
+ */
+#define current_cred() \
+        (current->cred)
+
+/**
+ * __task_cred - Access another task's credentials
+ * @task: The task to query
+ *
+ * Access the credentials of another task.  The caller must hold the
+ * RCU readlock.
+ *
+ * The caller must make sure task doesn't go away, either by holding a ref on
+ * task or by holding tasklist_lock to prevent it from being unlinked.
+ */
+#define __task_cred(task) \
+        ((const struct cred *)(rcu_dereference((task)->cred)))
+
+/**
+ * get_task_cred - Get another task's credentials
+ * @task: The task to query
+ *
+ * Get the credentials of a task, pinning them so that they can't go away.
+ * Accessing a task's credentials directly is not permitted.
+ *
+ * The caller must make sure task doesn't go away, either by holding a ref on
+ * task or by holding tasklist_lock to prevent it from being unlinked.
+ */
+#define get_task_cred(task)                             \
+({                                                      \
+        struct cred *__cred;                            \
+        rcu_read_lock();                                \
+        __cred = (struct cred *) __task_cred((task));   \
+        get_cred(__cred);                               \
+        rcu_read_unlock();                              \
+        __cred;                                         \
+})
+
+/**
+ * get_current_cred - Get the current task's credentials
+ *
+ * Get the credentials of the current task, pinning them so that they can't go
+ * away.  Accessing the current task's credentials directly is not permitted.
+ */
+#define get_current_cred()                              \
+        (get_cred(current_cred()))
+
+/**
+ * get_current_user - Get the current task's user_struct
+ *
+ * Get the user record of the current task, pinning it so that it can't go
+ * away.
+ */
+#define get_current_user()                              \
+({                                                      \
+        struct user_struct *__u;                        \
+        struct cred *__cred;                            \
+        __cred = (struct cred *) current_cred();        \
+        __u = get_uid(__cred->user);                    \
+        __u;                                            \
+})
+
+/**
+ * get_current_groups - Get the current task's supplementary group list
+ *
+ * Get the supplementary group list of the current task, pinning it so that it
+ * can't go away.
+ */
+#define get_current_groups()                            \
+({                                                      \
+        struct group_info *__groups;                    \
+        struct cred *__cred;                            \
+        __cred = (struct cred *) current_cred();        \
+        __groups = get_group_info(__cred->group_info);  \
+        __groups;                                       \
+})
+
+#define task_cred_xxx(task, xxx)                \
+({                                              \
+        __typeof__(task->cred->xxx) ___val;     \
+        rcu_read_lock();                        \
+        ___val = __task_cred((task))->xxx;      \
+        rcu_read_unlock();                      \
+        ___val;                                 \
+})
+
+#define task_uid(task)          (task_cred_xxx((task), uid))
+#define task_euid(task)         (task_cred_xxx((task), euid))
+
+#define current_cred_xxx(xxx)                   \
+({                                              \
+        current->cred->xxx;                     \
+})
+
+#define current_uid()           (current_cred_xxx(uid))
+#define current_gid()           (current_cred_xxx(gid))
+#define current_euid()          (current_cred_xxx(euid))
+#define current_egid()          (current_cred_xxx(egid))
+#define current_suid()          (current_cred_xxx(suid))
+#define current_sgid()          (current_cred_xxx(sgid))
+#define current_fsuid()         (current_cred_xxx(fsuid))
+#define current_fsgid()         (current_cred_xxx(fsgid))
+#define current_cap()           (current_cred_xxx(cap_effective))
+#define current_user()          (current_cred_xxx(user))
+#define current_security()      (current_cred_xxx(security))
+
+#define current_uid_gid(_uid, _gid)             \
+do {                                            \
+        const struct cred *__cred;              \
+        __cred = current_cred();                \
+        *(_uid) = __cred->uid;                  \
+        *(_gid) = __cred->gid;                  \
+} while(0)
+
+#define current_euid_egid(_euid, _egid)         \
+do {                                            \
+        const struct cred *__cred;              \
+        __cred = current_cred();                \
+        *(_euid) = __cred->euid;                \
+        *(_egid) = __cred->egid;                \
+} while(0)
+
+#define current_fsuid_fsgid(_fsuid, _fsgid)     \
+do {                                            \
+        const struct cred *__cred;              \
+        __cred = current_cred();                \
+        *(_fsuid) = __cred->fsuid;              \
+        *(_fsgid) = __cred->fsgid;              \
+} while(0)
+
 #endif /* _LINUX_CRED_H */