[PATCH] LSM: Revive security_task_alloc() hook and per "struct task_struct" security blob.
From: penguin-kernel@I-love.SAKURA.ne.jp (Tetsuo Handa)
Date: 2017-03-17 10:37:28
Subsystem:
exec & binfmt api, elf, memory management - core, scheduler, security subsystem, the rest · Maintainers:
Kees Cook, Andrew Morton, David Hildenbrand, Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
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@I-love.SAKURA.ne.jp> Acked-by: John Johansen <john.johansen@canonical.com> Acked-by: Serge Hallyn <serge@hallyn.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Tested-by: Djalal Harouni <redacted> Cc: Paul Moore <paul@paul-moore.com> Cc: Stephen Smalley <redacted> Cc: Eric Paris <redacted> Cc: Kees Cook <redacted> Cc: James Morris <redacted> Cc: Jos? Bollo <redacted> --- 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),
--
1.8.3.1
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