CRED: Detach the credentials from task_struct

Detach the credentials from task_struct, duplicating them in copy_process()
and releasing them in __put_task_struct().

Signed-off-by: David Howells <[email protected]>
Acked-by: James Morris <[email protected]>
Acked-by: Serge Hallyn <[email protected]>
Signed-off-by: James Morris <[email protected]>

include/linux/cred.h

@@ -158,4 +158,33 @@ do {						\
 	*(_gid) = current->cred->fsgid;		\
 } while(0)
 
+extern void __put_cred(struct cred *);
+extern int copy_creds(struct task_struct *, unsigned long);
+
+/**
+ * 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.
+ */
+static inline struct cred *get_cred(struct cred *cred)
+{
+	atomic_inc(&cred->usage);
+	return 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.
+ */
+static inline void put_cred(struct cred *cred)
+{
+	if (atomic_dec_and_test(&(cred)->usage))
+		__put_cred(cred);
+}
+
 #endif /* _LINUX_CRED_H */

include/linux/init_task.h

@@ -115,19 +115,6 @@ extern struct group_info init_groups;
 
 extern struct cred init_cred;
 
-#define INIT_CRED(p)						\
-{								\
-	.usage			= ATOMIC_INIT(3),		\
-	.securebits		= SECUREBITS_DEFAULT,		\
-	.cap_inheritable	= CAP_INIT_INH_SET,		\
-	.cap_permitted		= CAP_FULL_SET,			\
-	.cap_effective		= CAP_INIT_EFF_SET,		\
-	.cap_bset		= CAP_INIT_BSET,		\
-	.user			= INIT_USER,			\
-	.group_info		= &init_groups,			\
-	.lock			= __SPIN_LOCK_UNLOCKED(p.lock),	\
-}
-
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -162,8 +149,7 @@ extern struct cred init_cred;
 	.children	= LIST_HEAD_INIT(tsk.children),			\
 	.sibling	= LIST_HEAD_INIT(tsk.sibling),			\
 	.group_leader	= &tsk,						\
-	.__temp_cred	= INIT_CRED(tsk.__temp_cred),			\
-	.cred		= &tsk.__temp_cred,				\
+	.cred		= &init_cred,					\
 	.comm		= "swapper",					\
 	.thread		= INIT_THREAD,					\
 	.fs		= &init_fs,					\

include/linux/sched.h

@@ -1151,7 +1151,6 @@ struct task_struct {
 	struct list_head cpu_timers[3];
 
 /* process credentials */
-	struct cred __temp_cred __deprecated; /* temporary credentials to be removed */
 	struct cred *cred;	/* actual/objective task credentials */
 
 	char comm[TASK_COMM_LEN]; /* executable name excluding path

include/linux/security.h

@@ -593,15 +593,15 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
  *	manual page for definitions of the @clone_flags.
  *	@clone_flags contains the flags indicating what should be shared.
  *	Return 0 if permission is granted.
- * @task_alloc_security:
- *	@p contains the task_struct for child process.
- *	Allocate and attach a security structure to the p->security field. The
- *	security field is initialized to NULL when the task structure is
+ * @cred_alloc_security:
+ *	@cred contains the cred struct for child process.
+ *	Allocate and attach a security structure to the cred->security field.
+ *	The security field is initialized to NULL when the task structure is
  *	allocated.
  *	Return 0 if operation was successful.
- * @task_free_security:
- *	@p contains the task_struct for process.
- *	Deallocate and clear the p->security field.
+ * @cred_free:
+ *	@cred points to the credentials.
+ *	Deallocate and clear the cred->security field in a set of credentials.
  * @task_setuid:
  *	Check permission before setting one or more of the user identity
  *	attributes of the current process.  The @flags parameter indicates
@@ -1405,8 +1405,8 @@ struct security_operations {
 	int (*dentry_open) (struct file *file);
 
 	int (*task_create) (unsigned long clone_flags);
-	int (*task_alloc_security) (struct task_struct *p);
-	void (*task_free_security) (struct task_struct *p);
+	int (*cred_alloc_security) (struct cred *cred);
+	void (*cred_free) (struct cred *cred);
 	int (*task_setuid) (uid_t id0, uid_t id1, uid_t id2, int flags);
 	int (*task_post_setuid) (uid_t old_ruid /* or fsuid */ ,
 				 uid_t old_euid, uid_t old_suid, int flags);
@@ -1660,8 +1660,8 @@ int security_file_send_sigiotask(struct task_struct *tsk,
 int security_file_receive(struct file *file);
 int security_dentry_open(struct file *file);
 int security_task_create(unsigned long clone_flags);
-int security_task_alloc(struct task_struct *p);
-void security_task_free(struct task_struct *p);
+int security_cred_alloc(struct cred *cred);
+void security_cred_free(struct cred *cred);
 int security_task_setuid(uid_t id0, uid_t id1, uid_t id2, int flags);
 int security_task_post_setuid(uid_t old_ruid, uid_t old_euid,
 			      uid_t old_suid, int flags);
@@ -2181,12 +2181,12 @@ static inline int security_task_create(unsigned long clone_flags)
 	return 0;
 }
 
-static inline int security_task_alloc(struct task_struct *p)
+static inline int security_cred_alloc(struct cred *cred)
 {
 	return 0;
 }
 
-static inline void security_task_free(struct task_struct *p)
+static inline void security_cred_free(struct cred *cred)
 { }
 
 static inline int security_task_setuid(uid_t id0, uid_t id1, uid_t id2,

kernel/Makefile

@@ -9,7 +9,7 @@ obj-y     = sched.o fork.o exec_domain.o panic.o printk.o \
 	    rcupdate.o extable.o params.o posix-timers.o \
 	    kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
 	    hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
-	    notifier.o ksysfs.o pm_qos_params.o sched_clock.o
+	    notifier.o ksysfs.o pm_qos_params.o sched_clock.o cred.o
 
 CFLAGS_REMOVE_sched.o = -mno-spe
 

kernel/cred.c

@@ -0,0 +1,96 @@
+/* Task credentials management
+ *
+ * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([email protected])
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+#include <linux/module.h>
+#include <linux/cred.h>
+#include <linux/sched.h>
+#include <linux/key.h>
+#include <linux/keyctl.h>
+#include <linux/init_task.h>
+#include <linux/security.h>
+
+/*
+ * The initial credentials for the initial task
+ */
+struct cred init_cred = {
+	.usage			= ATOMIC_INIT(3),
+	.securebits		= SECUREBITS_DEFAULT,
+	.cap_inheritable	= CAP_INIT_INH_SET,
+	.cap_permitted		= CAP_FULL_SET,
+	.cap_effective		= CAP_INIT_EFF_SET,
+	.cap_bset		= CAP_INIT_BSET,
+	.user			= INIT_USER,
+	.group_info		= &init_groups,
+};
+
+/*
+ * The RCU callback to actually dispose of a set of credentials
+ */
+static void put_cred_rcu(struct rcu_head *rcu)
+{
+	struct cred *cred = container_of(rcu, struct cred, rcu);
+
+	BUG_ON(atomic_read(&cred->usage) != 0);
+
+	key_put(cred->thread_keyring);
+	key_put(cred->request_key_auth);
+	put_group_info(cred->group_info);
+	free_uid(cred->user);
+	security_cred_free(cred);
+	kfree(cred);
+}
+
+/**
+ * __put_cred - Destroy a set of credentials
+ * @sec: The record to release
+ *
+ * Destroy a set of credentials on which no references remain.
+ */
+void __put_cred(struct cred *cred)
+{
+	call_rcu(&cred->rcu, put_cred_rcu);
+}
+EXPORT_SYMBOL(__put_cred);
+
+/*
+ * Copy credentials for the new process created by fork()
+ */
+int copy_creds(struct task_struct *p, unsigned long clone_flags)
+{
+	struct cred *pcred;
+	int ret;
+
+	pcred = kmemdup(p->cred, sizeof(*p->cred), GFP_KERNEL);
+	if (!pcred)
+		return -ENOMEM;
+
+#ifdef CONFIG_SECURITY
+	pcred->security = NULL;
+#endif
+
+	ret = security_cred_alloc(pcred);
+	if (ret < 0) {
+		kfree(pcred);
+		return ret;
+	}
+
+	atomic_set(&pcred->usage, 1);
+	get_group_info(pcred->group_info);
+	get_uid(pcred->user);
+	key_get(pcred->thread_keyring);
+	key_get(pcred->request_key_auth);
+
+	atomic_inc(&pcred->user->processes);
+
+	/* RCU assignment is unneeded here as no-one can have accessed this
+	 * pointer yet, barring us */
+	p->cred = pcred;
+	return 0;
+}

kernel/fork.c

@@ -146,9 +146,7 @@ void __put_task_struct(struct task_struct *tsk)
 	WARN_ON(atomic_read(&tsk->usage));
 	WARN_ON(tsk == current);
 
-	security_task_free(tsk);
-	free_uid(tsk->__temp_cred.user);
-	put_group_info(tsk->__temp_cred.group_info);
+	put_cred(tsk->cred);
 	delayacct_tsk_free(tsk);
 
 	if (!profile_handoff_task(tsk))
@@ -969,7 +967,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
 	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
 #endif
-	p->cred = &p->__temp_cred;
 	retval = -EAGAIN;
 	if (atomic_read(&p->cred->user->processes) >=
 			p->signal->rlim[RLIMIT_NPROC].rlim_cur) {
@@ -978,9 +975,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 			goto bad_fork_free;
 	}
 
-	atomic_inc(&p->cred->user->__count);
-	atomic_inc(&p->cred->user->processes);
-	get_group_info(p->cred->group_info);
+	retval = copy_creds(p, clone_flags);
+	if (retval < 0)
+		goto bad_fork_free;
 
 	/*
 	 * If multiple threads are within copy_process(), then this check
@@ -1035,9 +1032,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	do_posix_clock_monotonic_gettime(&p->start_time);
 	p->real_start_time = p->start_time;
 	monotonic_to_bootbased(&p->real_start_time);
-#ifdef CONFIG_SECURITY
-	p->cred->security = NULL;
-#endif
 	p->io_context = NULL;
 	p->audit_context = NULL;
 	cgroup_fork(p);
@@ -1082,10 +1076,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	/* Perform scheduler related setup. Assign this task to a CPU. */
 	sched_fork(p, clone_flags);
 
-	if ((retval = security_task_alloc(p)))
-		goto bad_fork_cleanup_policy;
 	if ((retval = audit_alloc(p)))
-		goto bad_fork_cleanup_security;
+		goto bad_fork_cleanup_policy;
 	/* copy all the process information */
 	if ((retval = copy_semundo(clone_flags, p)))
 		goto bad_fork_cleanup_audit;
@@ -1284,8 +1276,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	exit_sem(p);
 bad_fork_cleanup_audit:
 	audit_free(p);
-bad_fork_cleanup_security:
-	security_task_free(p);
 bad_fork_cleanup_policy:
 #ifdef CONFIG_NUMA
 	mpol_put(p->mempolicy);
@@ -1298,9 +1288,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 bad_fork_cleanup_put_domain:
 	module_put(task_thread_info(p)->exec_domain->module);
 bad_fork_cleanup_count:
-	put_group_info(p->cred->group_info);
-	atomic_dec(&p->cred->user->processes);
-	free_uid(p->cred->user);
+	put_cred(p->cred);
 bad_fork_free:
 	free_task(p);
 fork_out:

security/capability.c

@@ -340,12 +340,12 @@ static int cap_task_create(unsigned long clone_flags)
 	return 0;
 }
 
-static int cap_task_alloc_security(struct task_struct *p)
+static int cap_cred_alloc_security(struct cred *cred)
 {
 	return 0;
 }
 
-static void cap_task_free_security(struct task_struct *p)
+static void cap_cred_free(struct cred *cred)
 {
 }
 
@@ -890,8 +890,8 @@ void security_fixup_ops(struct security_operations *ops)
 	set_to_cap_if_null(ops, file_receive);
 	set_to_cap_if_null(ops, dentry_open);
 	set_to_cap_if_null(ops, task_create);
-	set_to_cap_if_null(ops, task_alloc_security);
-	set_to_cap_if_null(ops, task_free_security);
+	set_to_cap_if_null(ops, cred_alloc_security);
+	set_to_cap_if_null(ops, cred_free);
 	set_to_cap_if_null(ops, task_setuid);
 	set_to_cap_if_null(ops, task_post_setuid);
 	set_to_cap_if_null(ops, task_setgid);

security/security.c

@@ -616,14 +616,14 @@ int security_task_create(unsigned long clone_flags)
 	return security_ops->task_create(clone_flags);
 }
 
-int security_task_alloc(struct task_struct *p)
+int security_cred_alloc(struct cred *cred)
 {
-	return security_ops->task_alloc_security(p);
+	return security_ops->cred_alloc_security(cred);
 }
 
-void security_task_free(struct task_struct *p)
+void security_cred_free(struct cred *cred)
 {
-	security_ops->task_free_security(p);
+	security_ops->cred_free(cred);
 }
 
 int security_task_setuid(uid_t id0, uid_t id1, uid_t id2, int flags)