Re: [PATCH ghak90 (was ghak32) V4 01/10] audit: collect audit task parameters

Guenter Roeck
2019-01-04T02:50:06Z

Hi Richard,

On Tue, Jul 31, 2018 at 04:07:36PM -0400, Richard Guy Briggs wrote:
> The audit-related parameters in struct task_struct should ideally be
> collected together and accessed through a standard audit API.
>
> Collect the existing loginuid, sessionid and audit_context together in a
> new struct audit_task_info called "audit" in struct task_struct.
>
> Use kmem_cache to manage this pool of memory.
> Un-inline audit_free() to be able to always recover that memory.
>
> See: https://github.com/linux-audit/audit-kernel/issues/81
>
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>

Overall I am not sure if keeping task_struct a bit smaller is worth
the added complexity, but I guess that is just me.

Anyway, couple of nitpicks. Please feel free to ignore, and my apologies
if some of all of the comments are duplicates.

Guenter

> ---
> include/linux/audit.h | 34 ++++++++++++++++++++++++----------
> include/linux/sched.h | 5 +----
> init/init_task.c | 3 +--
> init/main.c | 2 ++
> kernel/auditsc.c | 51 ++++++++++++++++++++++++++++++++++++++++++---------
> kernel/fork.c | 4 +++-
> 6 files changed, 73 insertions(+), 26 deletions(-)
>
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index 9334fbe..8964332 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -219,8 +219,15 @@ static inline void audit_log_task_info(struct audit_buffer *ab,
>
> /* These are defined in auditsc.c */
> /* Public API */

Not sure if the structure below belongs after "Public API".
Is it part of the public API ?

> +struct audit_task_info {
> + kuid_t loginuid;
> + unsigned int sessionid;
> + struct audit_context *ctx;
> +};

Add empty line ?

> +extern struct audit_task_info init_struct_audit;
> +extern void __init audit_task_init(void);
> extern int audit_alloc(struct task_struct *task);
> -extern void __audit_free(struct task_struct *task);
> +extern void audit_free(struct task_struct *task);
> extern void __audit_syscall_entry(int major, unsigned long a0, unsigned long a1,
> unsigned long a2, unsigned long a3);
> extern void __audit_syscall_exit(int ret_success, long ret_value);
> @@ -242,12 +249,15 @@ extern void audit_seccomp_actions_logged(const char *names,
>
> static inline void audit_set_context(struct task_struct *task, struct audit_context *ctx)
> {
> - task->audit_context = ctx;
> + task->audit->ctx = ctx;
> }
>
> static inline struct audit_context *audit_context(void)
> {
> - return current->audit_context;
> + if (current->audit)
> + return current->audit->ctx;
> + else
> + return NULL;

Unnecessary else (and static checkers may complain).

> }
>
> static inline bool audit_dummy_context(void)
> @@ -255,11 +265,7 @@ static inline bool audit_dummy_context(void)
> void *p = audit_context();
> return !p || *(int *)p;
> }
> -static inline void audit_free(struct task_struct *task)
> -{
> - if (unlikely(task->audit_context))
> - __audit_free(task);
> -}
> +
> static inline void audit_syscall_entry(int major, unsigned long a0,
> unsigned long a1, unsigned long a2,
> unsigned long a3)
> @@ -331,12 +337,18 @@ extern int auditsc_get_stamp(struct audit_context *ctx,
>
> static inline kuid_t audit_get_loginuid(struct task_struct *tsk)
> {
> - return tsk->loginuid;
> + if (tsk->audit)
> + return tsk->audit->loginuid;
> + else
> + return INVALID_UID;

Unnecessary else.

> }
>
> static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
> {
> - return tsk->sessionid;
> + if (tsk->audit)
> + return tsk->audit->sessionid;
> + else
> + return AUDIT_SID_UNSET;

Unnecessary else.

> }
>
> extern void __audit_ipc_obj(struct kern_ipc_perm *ipcp);
> @@ -461,6 +473,8 @@ static inline void audit_fanotify(unsigned int response)
> extern int audit_n_rules;
> extern int audit_signals;
> #else /* CONFIG_AUDITSYSCALL */
> +static inline void __init audit_task_init(void)
> +{ }
> static inline int audit_alloc(struct task_struct *task)
> {
> return 0;
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 87bf02d..e117272 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -30,7 +30,6 @@
> #include <linux/rseq.h>
>
> /* task_struct member predeclarations (sorted alphabetically): */
> -struct audit_context;
> struct backing_dev_info;
> struct bio_list;
> struct blk_plug;
> @@ -873,10 +872,8 @@ struct task_struct {
>
> struct callback_head *task_works;
>
> - struct audit_context *audit_context;
> #ifdef CONFIG_AUDITSYSCALL
> - kuid_t loginuid;
> - unsigned int sessionid;
> + struct audit_task_info *audit;
> #endif
> struct seccomp seccomp;
>
> diff --git a/init/init_task.c b/init/init_task.c
> index 74f60ba..4058840 100644
> --- a/init/init_task.c
> +++ b/init/init_task.c
> @@ -119,8 +119,7 @@ struct task_struct init_task
> .thread_group = LIST_HEAD_INIT(init_task.thread_group),
> .thread_node = LIST_HEAD_INIT(init_signals.thread_head),
> #ifdef CONFIG_AUDITSYSCALL
> - .loginuid = INVALID_UID,
> - .sessionid = AUDIT_SID_UNSET,
> + .audit = &init_struct_audit,
> #endif
> #ifdef CONFIG_PERF_EVENTS
> .perf_event_mutex = __MUTEX_INITIALIZER(init_task.perf_event_mutex),
> diff --git a/init/main.c b/init/main.c
> index 3b4ada1..6aba171 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -92,6 +92,7 @@
> #include <linux/rodata_test.h>
> #include <linux/jump_label.h>
> #include <linux/mem_encrypt.h>
> +#include <linux/audit.h>
>
> #include <asm/io.h>
> #include <asm/bugs.h>
> @@ -721,6 +722,7 @@ asmlinkage __visible void __init start_kernel(void)
> nsfs_init();
> cpuset_init();
> cgroup_init();
> + audit_task_init();
> taskstats_init_early();
> delayacct_init();
>
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index fb20746..88779a7 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -841,7 +841,7 @@ static inline struct audit_context *audit_take_context(struct task_struct *tsk,
> int return_valid,
> long return_code)
> {
> - struct audit_context *context = tsk->audit_context;
> + struct audit_context *context = tsk->audit->ctx;
>
> if (!context)
> return NULL;
> @@ -926,6 +926,15 @@ static inline struct audit_context *audit_alloc_context(enum audit_state state)
> return context;
> }
>
> +static struct kmem_cache *audit_task_cache;
> +
> +void __init audit_task_init(void)
> +{
> + audit_task_cache = kmem_cache_create("audit_task",
> + sizeof(struct audit_task_info),
> + 0, SLAB_PANIC, NULL);
> +}
> +
> /**
> * audit_alloc - allocate an audit context block for a task
> * @tsk: task
> @@ -940,17 +949,28 @@ int audit_alloc(struct task_struct *tsk)
> struct audit_context *context;
> enum audit_state state;
> char *key = NULL;
> + struct audit_task_info *info;
> +
> + info = kmem_cache_zalloc(audit_task_cache, GFP_KERNEL);
> + if (!info)
> + return -ENOMEM;
> + info->loginuid = audit_get_loginuid(current);
> + info->sessionid = audit_get_sessionid(current);
> + tsk->audit = info;
>
> if (likely(!audit_ever_enabled))
> return 0; /* Return if not auditing. */
>
> state = audit_filter_task(tsk, &key);
> if (state == AUDIT_DISABLED) {
> + audit_set_context(tsk, NULL);
> clear_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
> return 0;
> }
>
> if (!(context = audit_alloc_context(state))) {
> + tsk->audit = NULL;
> + kmem_cache_free(audit_task_cache, info);
> kfree(key);
> audit_log_lost("out of memory in audit_alloc");
> return -ENOMEM;
> @@ -962,6 +982,12 @@ int audit_alloc(struct task_struct *tsk)
> return 0;
> }
>
> +struct audit_task_info init_struct_audit = {
> + .loginuid = INVALID_UID,
> + .sessionid = AUDIT_SID_UNSET,
> + .ctx = NULL,
> +};
> +
> static inline void audit_free_context(struct audit_context *context)
> {
> audit_free_names(context);
> @@ -1469,26 +1495,33 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
> }
>
> /**
> - * __audit_free - free a per-task audit context
> + * audit_free - free a per-task audit context
> * @tsk: task whose audit context block to free
> *
> * Called from copy_process and do_exit
> */
> -void __audit_free(struct task_struct *tsk)
> +void audit_free(struct task_struct *tsk)
> {
> struct audit_context *context;
> + struct audit_task_info *info;
>
> context = audit_take_context(tsk, 0, 0);
> - if (!context)
> - return;
> -
> /* Check for system calls that do not go through the exit
> * function (e.g., exit_group), then free context block.
> * We use GFP_ATOMIC here because we might be doing this
> * in the context of the idle thread */
> /* that can happen only if we are called from do_exit() */
> - if (context->in_syscall && context->current_state == AUDIT_RECORD_CONTEXT)
> + if (context && context->in_syscall &&
> + context->current_state == AUDIT_RECORD_CONTEXT)
> audit_log_exit(context, tsk);
> + /* Freeing the audit_task_info struct must be performed after
> + * audit_log_exit() due to need for loginuid and sessionid.
> + */
> + info = tsk->audit;
> + tsk->audit = NULL;
> + kmem_cache_free(audit_task_cache, info);
> + if (!context)
> + return;
> if (!list_empty(&context->killed_trees))
> audit_kill_trees(&context->killed_trees);

Looks kind of terrible with the repeated check if context is NULL.
Maybe reorder ?

context = audit_take_context(tsk, 0, 0);
if (context) {
/* do all the context work */
}
kmem_cache_free(audit_task_cache, tsk->audit);
tsk->audit = NULL; // is that even necessary ?

If "info" is really needed, ie if tsk (and tsk->audit) can be accessed
from another thread in parallel, I'd be a bit concerned about the lack
of sync() or similar after clearing tsk->audit.

Another option might have been to separate audit_free() into
audit_free_context() and audit_free_info().

>
> @@ -2071,8 +2104,8 @@ int audit_set_loginuid(kuid_t loginuid)
> sessionid = (unsigned int)atomic_inc_return(&session_id);
> }
>
> - task->sessionid = sessionid;
> - task->loginuid = loginuid;
> + task->audit->sessionid = sessionid;
> + task->audit->loginuid = loginuid;
> out:
> audit_log_set_loginuid(oldloginuid, loginuid, oldsessionid, sessionid, rc);
> return rc;
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 9440d61..1bfb0ff 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1721,7 +1721,9 @@ static __latent_entropy struct task_struct *copy_process(
> p->start_time = ktime_get_ns();
> p->real_start_time = ktime_get_boot_ns();
> p->io_context = NULL;
> - audit_set_context(p, NULL);
> +#ifdef CONFIG_AUDITSYSCALL
> + p->audit = NULL;
> +#endif /* CONFIG_AUDITSYSCALL */

audit_alloc() is called a bit later and sets p->audit, so I don't think
this is really necessary.

> cgroup_fork(p);
> #ifdef CONFIG_NUMA
> p->mempolicy = mpol_dup(p->mempolicy);