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.

Kees Cook committed 12 years ago

Commit 3ba25301 parent dbd95211 file · +25 −11Browse files

Unified · Split

kernel/seccomp.c+25−11

@@ -173,21 +173,24 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) · 172 unmodified lines
173	173	*/
174	174	static u32 seccomp_run_filters(int syscall)
175	175	{
176		− struct seccomp_filter *f;
	176	+ struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter);
177	177	struct seccomp_data sd;
178	178	u32 ret = SECCOMP_RET_ALLOW;
179	179
180	180	/* Ensure unexpected behavior doesn't result in failing open. */
181		− if (WARN_ON(current->seccomp.filter == NULL))
	181	+ if (unlikely(WARN_ON(f == NULL)))
182	182	return SECCOMP_RET_KILL;
183	183
	184	+ /* Make sure cross-thread synced filter points somewhere sane. */
	185	+ smp_read_barrier_depends();
	186	+
184	187	populate_seccomp_data(&sd);
185	188
186	189	/*
187	190	* All filters in the list are evaluated and the lowest BPF return
188	191	* value always takes priority (ignoring the DATA).
189	192	*/
190		− for (f = current->seccomp.filter; f; f = f->prev) {
	193	+ for (; f; f = f->prev) {
191	194	u32 cur_ret = SK_RUN_FILTER(f->prog, (void *)&sd);
192	195
193	196	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) · 13 unmodified lines
207	210	return true;
208	211	}
209	212
210		−static inline void seccomp_assign_mode(unsigned long seccomp_mode)
	213	+static inline void seccomp_assign_mode(struct task_struct *task,
	214	+ unsigned long seccomp_mode)
211	215	{
212		− BUG_ON(!spin_is_locked(&current->sighand->siglock));
	216	+ BUG_ON(!spin_is_locked(&task->sighand->siglock));
213	217
214		− current->seccomp.mode = seccomp_mode;
215		− set_tsk_thread_flag(current, TIF_SECCOMP);
	218	+ task->seccomp.mode = seccomp_mode;
	219	+ /*
	220	+ * Make sure TIF_SECCOMP cannot be set before the mode (and
	221	+ * filter) is set.
	222	+ */
	223	+ smp_mb__before_atomic();
	224	+ set_tsk_thread_flag(task, TIF_SECCOMP);
216	225	}
217	226
218	227	#ifdef CONFIG_SECCOMP_FILTER
@@ -435,12 +444,17 @@ static int mode1_syscalls_32[] = { · 216 unmodified lines
435	444
436	445	int __secure_computing(int this_syscall)
437	446	{
438		− int mode = current->seccomp.mode;
439	447	int exit_sig = 0;
440	448	int *syscall;
441	449	u32 ret;
442	450
443		− switch (mode) {
	451	+ /*
	452	+ * Make sure that any changes to mode from another thread have
	453	+ * been seen after TIF_SECCOMP was seen.
	454	+ */
	455	+ rmb();
	456	+
	457	+ switch (current->seccomp.mode) {
444	458	case SECCOMP_MODE_STRICT:
445	459	syscall = mode1_syscalls;
446	460	#ifdef CONFIG_COMPAT
@@ -545,7 +559,7 @@ static long seccomp_set_mode_strict(void) · 98 unmodified lines
545	559	#ifdef TIF_NOTSC
546	560	disable_TSC();
547	561	#endif
548		− seccomp_assign_mode(seccomp_mode);
	562	+ seccomp_assign_mode(current, seccomp_mode);
549	563	ret = 0;
550	564
551	565	out:
@@ -595,7 +609,7 @@ static long seccomp_set_mode_filter(unsigned int flags, · 43 unmodified lines
595	609	/* Do not free the successfully attached filter. */
596	610	prepared = NULL;
597	611
598		− seccomp_assign_mode(seccomp_mode);
	612	+ seccomp_assign_mode(current, seccomp_mode);
599	613	out:
600	614	spin_unlock_irq(&current->sighand->siglock);
601	615	seccomp_filter_free(prepared);