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: Kees Cook <keescook@chromium.org> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Andy Lutomirski <luto@amacapital.net>
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1 changed files with 25 additions and 11 deletions
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@ -173,21 +173,24 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
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*/
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static u32 seccomp_run_filters(int syscall)
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{
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struct seccomp_filter *f;
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struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter);
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struct seccomp_data sd;
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u32 ret = SECCOMP_RET_ALLOW;
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/* Ensure unexpected behavior doesn't result in failing open. */
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if (WARN_ON(current->seccomp.filter == NULL))
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if (unlikely(WARN_ON(f == NULL)))
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return SECCOMP_RET_KILL;
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/* Make sure cross-thread synced filter points somewhere sane. */
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smp_read_barrier_depends();
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populate_seccomp_data(&sd);
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/*
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* All filters in the list are evaluated and the lowest BPF return
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* value always takes priority (ignoring the DATA).
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*/
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for (f = current->seccomp.filter; f; f = f->prev) {
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for (; f; f = f->prev) {
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u32 cur_ret = SK_RUN_FILTER(f->prog, (void *)&sd);
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if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
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@ -207,12 +210,18 @@ static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode)
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return true;
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}
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static inline void seccomp_assign_mode(unsigned long seccomp_mode)
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static inline void seccomp_assign_mode(struct task_struct *task,
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unsigned long seccomp_mode)
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{
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BUG_ON(!spin_is_locked(¤t->sighand->siglock));
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BUG_ON(!spin_is_locked(&task->sighand->siglock));
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current->seccomp.mode = seccomp_mode;
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set_tsk_thread_flag(current, TIF_SECCOMP);
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task->seccomp.mode = seccomp_mode;
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/*
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* Make sure TIF_SECCOMP cannot be set before the mode (and
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* filter) is set.
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*/
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smp_mb__before_atomic();
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set_tsk_thread_flag(task, TIF_SECCOMP);
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}
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#ifdef CONFIG_SECCOMP_FILTER
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@ -435,12 +444,17 @@ static int mode1_syscalls_32[] = {
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int __secure_computing(int this_syscall)
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{
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int mode = current->seccomp.mode;
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int exit_sig = 0;
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int *syscall;
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u32 ret;
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switch (mode) {
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/*
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* Make sure that any changes to mode from another thread have
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* been seen after TIF_SECCOMP was seen.
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*/
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rmb();
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switch (current->seccomp.mode) {
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case SECCOMP_MODE_STRICT:
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syscall = mode1_syscalls;
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#ifdef CONFIG_COMPAT
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@ -545,7 +559,7 @@ static long seccomp_set_mode_strict(void)
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#ifdef TIF_NOTSC
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disable_TSC();
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#endif
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seccomp_assign_mode(seccomp_mode);
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seccomp_assign_mode(current, seccomp_mode);
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ret = 0;
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out:
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@ -595,7 +609,7 @@ static long seccomp_set_mode_filter(unsigned int flags,
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/* Do not free the successfully attached filter. */
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prepared = NULL;
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seccomp_assign_mode(seccomp_mode);
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seccomp_assign_mode(current, seccomp_mode);
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out:
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spin_unlock_irq(¤t->sighand->siglock);
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seccomp_filter_free(prepared);
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