Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 3ba2530c authored by Kees Cook's avatar Kees Cook
Browse files

seccomp: allow mode setting across threads 



This changes the mode setting helper to allow threads to change the
seccomp mode from another thread. We must maintain barriers to keep
TIF_SECCOMP synchronized with the rest of the seccomp state.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Reviewed-by: default avatarAndy Lutomirski <luto@amacapital.net>
parent dbd95212

kernel/seccomp.c

+25 −11
Original line number Original line Diff line number Diff line
@@ -173,21 +173,24 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) 
 */

 */

static u32 seccomp_run_filters(int syscall)

static u32 seccomp_run_filters(int syscall)

{

{

	struct seccomp_filter *f;

	struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter);

	struct seccomp_data sd;

	struct seccomp_data sd;

	u32 ret = SECCOMP_RET_ALLOW;

	u32 ret = SECCOMP_RET_ALLOW;





	/* Ensure unexpected behavior doesn't result in failing open. */

	/* Ensure unexpected behavior doesn't result in failing open. */

	if (WARN_ON(current->seccomp.filter == NULL))

	if (unlikely(WARN_ON(f == NULL)))

		return SECCOMP_RET_KILL;

		return SECCOMP_RET_KILL;





	/* Make sure cross-thread synced filter points somewhere sane. */

	smp_read_barrier_depends();



	populate_seccomp_data(&sd);

	populate_seccomp_data(&sd);





	/*

	/*

	 * All filters in the list are evaluated and the lowest BPF return

	 * All filters in the list are evaluated and the lowest BPF return

	 * value always takes priority (ignoring the DATA).

	 * value always takes priority (ignoring the DATA).

	 */

	 */

	for (f = current->seccomp.filter; f; f = f->prev) {

	for (; f; f = f->prev) {

		u32 cur_ret = SK_RUN_FILTER(f->prog, (void *)&sd);

		u32 cur_ret = SK_RUN_FILTER(f->prog, (void *)&sd);





		if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))

		if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
@@ -207,12 +210,18 @@ static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) 
	return true;

	return true;

}

}





static inline void seccomp_assign_mode(unsigned long seccomp_mode)

static inline void seccomp_assign_mode(struct task_struct *task,

				       unsigned long seccomp_mode)

{

{

	BUG_ON(!spin_is_locked(&current->sighand->siglock));

	BUG_ON(!spin_is_locked(&task->sighand->siglock));





	current->seccomp.mode = seccomp_mode;

	task->seccomp.mode = seccomp_mode;

	set_tsk_thread_flag(current, TIF_SECCOMP);

	/*

	 * Make sure TIF_SECCOMP cannot be set before the mode (and

	 * filter) is set.

	 */

	smp_mb__before_atomic();

	set_tsk_thread_flag(task, TIF_SECCOMP);

}

}





#ifdef CONFIG_SECCOMP_FILTER

#ifdef CONFIG_SECCOMP_FILTER
@@ -435,12 +444,17 @@ static int mode1_syscalls_32[] = { 




int __secure_computing(int this_syscall)

int __secure_computing(int this_syscall)

{

{

	int mode = current->seccomp.mode;

	int exit_sig = 0;

	int exit_sig = 0;

	int *syscall;

	int *syscall;

	u32 ret;

	u32 ret;





	switch (mode) {

	/*

	 * Make sure that any changes to mode from another thread have

	 * been seen after TIF_SECCOMP was seen.

	 */

	rmb();



	switch (current->seccomp.mode) {

	case SECCOMP_MODE_STRICT:

	case SECCOMP_MODE_STRICT:

		syscall = mode1_syscalls;

		syscall = mode1_syscalls;

#ifdef CONFIG_COMPAT

#ifdef CONFIG_COMPAT
@@ -545,7 +559,7 @@ static long seccomp_set_mode_strict(void) 
#ifdef TIF_NOTSC

#ifdef TIF_NOTSC

	disable_TSC();

	disable_TSC();

#endif

#endif

	seccomp_assign_mode(seccomp_mode);

	seccomp_assign_mode(current, seccomp_mode);

	ret = 0;

	ret = 0;





out:

out:
@@ -595,7 +609,7 @@ static long seccomp_set_mode_filter(unsigned int flags, 
	/* Do not free the successfully attached filter. */

	/* Do not free the successfully attached filter. */

	prepared = NULL;

	prepared = NULL;





	seccomp_assign_mode(seccomp_mode);

	seccomp_assign_mode(current, seccomp_mode);

out:

out:

	spin_unlock_irq(&current->sighand->siglock);

	spin_unlock_irq(&current->sighand->siglock);

	seccomp_filter_free(prepared);

	seccomp_filter_free(prepared);