[PATCH] LSM: Revive security_task_alloc() hook and per "struct task_struct" security blob.
Casey Schaufler
casey at schaufler-ca.com
Mon Mar 13 16:08:08 UTC 2017
On 3/11/2017 8:35 PM, Tetsuo Handa wrote:
> 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. PTAGS LSM module
> and CaitSith LSM module which are currently under proposal for inclusion
> also want to use it. Therefore, it will be time to revive
> security_task_alloc() hook and "struct task_struct"->security field.
>
> 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: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
> Acked-by: John Johansen <john.johansen at canonical.com>
> Tested-by: Djalal Harouni <tixxdz at gmail.com>
> Cc: Paul Moore <paul at paul-moore.com>
> Cc: Stephen Smalley <sds at tycho.nsa.gov>
> Cc: Eric Paris <eparis at parisplace.org>
> Cc: Casey Schaufler <casey at schaufler-ca.com>
Acked-by: Casey Schaufler <casey at schaufler-ca.com>
> Cc: Kees Cook <keescook at chromium.org>
> Cc: James Morris <james.l.morris at oracle.com>
> Cc: Serge E. Hallyn <serge at hallyn.com>
> Cc: José Bollo <jobol at nonadev.net>
> ---
> include/linux/init_task.h | 7 +++++++
> include/linux/lsm_hooks.h | 9 ++++++++-
> include/linux/sched.h | 4 ++++
> include/linux/security.h | 7 +++++++
> kernel/fork.c | 7 ++++++-
> security/security.c | 6 ++++++
> 6 files changed, 38 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/init_task.h b/include/linux/init_task.h
> index 91d9049..926f2f5 100644
> --- a/include/linux/init_task.h
> +++ b/include/linux/init_task.h
> @@ -210,6 +210,12 @@
> # 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 @@
> INIT_VTIME(tsk) \
> INIT_NUMA_BALANCING(tsk) \
> INIT_KASAN(tsk) \
> + INIT_TASK_SECURITY \
> }
>
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 1aa6333..a4193c3 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -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 @@
> 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;
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index d67eee8..71b8df3 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1038,6 +1038,10 @@ struct task_struct {
> /* 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;
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 97df7ba..af675b5 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -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)
> { }
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 6c463c80..3d32513 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -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:
> diff --git a/security/security.c b/security/security.c
> index d6d18a3..5b6cdd0 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -930,6 +930,11 @@ int security_task_create(unsigned long clone_flags)
> return call_int_hook(task_create, 0, clone_flags);
> }
>
> +int security_task_alloc(struct task_struct *task, unsigned long clone_flags)
> +{
> + return call_int_hook(task_alloc, 0, task, clone_flags);
> +}
> +
> void security_task_free(struct task_struct *task)
> {
> call_void_hook(task_free, task);
> @@ -1770,6 +1775,7 @@ struct security_hook_heads security_hook_heads __lsm_ro_after_init = {
> .file_receive = LIST_HEAD_INIT(security_hook_heads.file_receive),
> .file_open = LIST_HEAD_INIT(security_hook_heads.file_open),
> .task_create = LIST_HEAD_INIT(security_hook_heads.task_create),
> + .task_alloc = LIST_HEAD_INIT(security_hook_heads.task_alloc),
> .task_free = LIST_HEAD_INIT(security_hook_heads.task_free),
> .cred_alloc_blank =
> LIST_HEAD_INIT(security_hook_heads.cred_alloc_blank),
--
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