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Commit e4e55b47 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by James Morris
Browse files

LSM: Revive security_task_alloc() hook and per "struct task_struct" security blob. 



We switched from "struct task_struct"->security to "struct cred"->security
in Linux 2.6.29. But not all LSM modules were happy with that change.
TOMOYO LSM module is an example which want to use per "struct task_struct"
security blob, for TOMOYO's security context is defined based on "struct
task_struct" rather than "struct cred". AppArmor LSM module is another
example which want to use it, for AppArmor is currently abusing the cred
a little bit to store the change_hat and setexeccon info. Although
security_task_free() hook was revived in Linux 3.4 because Yama LSM module
wanted to release per "struct task_struct" security blob,
security_task_alloc() hook and "struct task_struct"->security field were
not revived. Nowadays, we are getting proposals of lightweight LSM modules
which want to use per "struct task_struct" security blob.

We are already allowing multiple concurrent LSM modules (up to one fully
armored module which uses "struct cred"->security field or exclusive hooks
like security_xfrm_state_pol_flow_match(), plus unlimited number of
lightweight modules which do not use "struct cred"->security nor exclusive
hooks) as long as they are built into the kernel. But this patch does not
implement variable length "struct task_struct"->security field which will
become needed when multiple LSM modules want to use "struct task_struct"->
security field. Although it won't be difficult to implement variable length
"struct task_struct"->security field, let's think about it after we merged
this patch.

Signed-off-by: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: default avatarJohn Johansen <john.johansen@canonical.com>
Acked-by: default avatarSerge Hallyn <serge@hallyn.com>
Acked-by: default avatarCasey Schaufler <casey@schaufler-ca.com>
Tested-by: default avatarDjalal Harouni <tixxdz@gmail.com>
Acked-by: default avatarJosé Bollo <jobol@nonadev.net>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Eric Paris <eparis@parisplace.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: James Morris <james.l.morris@oracle.com>
Cc: José Bollo <jobol@nonadev.net>
Signed-off-by: default avatarJames Morris <james.l.morris@oracle.com>
parent 840c91dc

include/linux/init_task.h

+7 −0
Original line number Diff line number Diff line
@@ -210,6 +210,12 @@ extern struct cred init_cred; 
# define INIT_TASK_TI(tsk)

#endif



#ifdef CONFIG_SECURITY

#define INIT_TASK_SECURITY .security = NULL,

#else

#define INIT_TASK_SECURITY

#endif



/*

 *  INIT_TASK is used to set up the first task table, touch at

 * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -288,6 +294,7 @@ extern struct cred init_cred; 
	INIT_VTIME(tsk)							\

	INIT_NUMA_BALANCING(tsk)					\

	INIT_KASAN(tsk)							\

	INIT_TASK_SECURITY						\

}

include/linux/lsm_hooks.h

+8 −1
Original line number Diff line number Diff line
@@ -533,8 +533,13 @@ 
 *	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:

 *	@task task being allocated.

 *	@clone_flags contains the flags indicating what should be shared.

 *	Handle allocation of task-related resources.

 *	Returns a zero on success, negative values on failure.

 * @task_free:

 *	@task task being freed

 *	@task task about to be freed.

 *	Handle release of task-related resources. (Note that this can be called

 *	from interrupt context.)

 * @cred_alloc_blank:
@@ -1482,6 +1487,7 @@ union security_list_options { 
	int (*file_open)(struct file *file, const struct cred *cred);



	int (*task_create)(unsigned long clone_flags);

	int (*task_alloc)(struct task_struct *task, unsigned long clone_flags);

	void (*task_free)(struct task_struct *task);

	int (*cred_alloc_blank)(struct cred *cred, gfp_t gfp);

	void (*cred_free)(struct cred *cred);
@@ -1748,6 +1754,7 @@ struct security_hook_heads { 
	struct list_head file_receive;

	struct list_head file_open;

	struct list_head task_create;

	struct list_head task_alloc;

	struct list_head task_free;

	struct list_head cred_alloc_blank;

	struct list_head cred_free;

include/linux/sched.h

+4 −0
Original line number Diff line number Diff line
@@ -1037,6 +1037,10 @@ struct task_struct { 
#ifdef CONFIG_THREAD_INFO_IN_TASK

	/* A live task holds one reference: */

	atomic_t			stack_refcount;

#endif

#ifdef CONFIG_SECURITY

	/* Used by LSM modules for access restriction: */

	void				*security;

#endif

	/* CPU-specific state of this task: */

	struct thread_struct		thread;

include/linux/security.h

+7 −0
Original line number Diff line number Diff line
@@ -308,6 +308,7 @@ int security_file_send_sigiotask(struct task_struct *tsk, 
int security_file_receive(struct file *file);

int security_file_open(struct file *file, const struct cred *cred);

int security_task_create(unsigned long clone_flags);

int security_task_alloc(struct task_struct *task, unsigned long clone_flags);

void security_task_free(struct task_struct *task);

int security_cred_alloc_blank(struct cred *cred, gfp_t gfp);

void security_cred_free(struct cred *cred);
@@ -861,6 +862,12 @@ static inline int security_task_create(unsigned long clone_flags) 
	return 0;

}



static inline int security_task_alloc(struct task_struct *task,

				      unsigned long clone_flags)

{

	return 0;

}



static inline void security_task_free(struct task_struct *task)

{ }

kernel/fork.c

+6 −1
Original line number Diff line number Diff line
@@ -1679,9 +1679,12 @@ static __latent_entropy struct task_struct *copy_process( 
		goto bad_fork_cleanup_perf;

	/* copy all the process information */

	shm_init_task(p);

	retval = copy_semundo(clone_flags, p);

	retval = security_task_alloc(p, clone_flags);

	if (retval)

		goto bad_fork_cleanup_audit;

	retval = copy_semundo(clone_flags, p);

	if (retval)

		goto bad_fork_cleanup_security;

	retval = copy_files(clone_flags, p);

	if (retval)

		goto bad_fork_cleanup_semundo;
@@ -1903,6 +1906,8 @@ static __latent_entropy struct task_struct *copy_process( 
	exit_files(p); /* blocking */

bad_fork_cleanup_semundo:

	exit_sem(p);

bad_fork_cleanup_security:

	security_task_free(p);

bad_fork_cleanup_audit:

	audit_free(p);

bad_fork_cleanup_perf: