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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>
This commit is contained in:
Kees Cook 2014-06-27 15:01:35 -07:00
parent dbd952127d
commit 3ba2530cc0
1 changed files with 25 additions and 11 deletions
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36
kernel/seccomp.c
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@ -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);