lkml.org 
[lkml]   [2014]   [Jul]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v10 10/11] seccomp: allow mode setting across threads
Date
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>
---
kernel/seccomp.c | 36 +++++++++++++++++++++++++-----------
1 file changed, 25 insertions(+), 11 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 6087e018155c..c6bd5f196d9f 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -173,21 +173,24 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
*/
static u32 seccomp_run_filters(int syscall)
{
- struct seccomp_filter *f;
+ struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter);
struct seccomp_data sd;
u32 ret = SECCOMP_RET_ALLOW;

/* 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;

+ /* Make sure cross-thread synced filter points somewhere sane. */
+ smp_read_barrier_depends();
+
populate_seccomp_data(&sd);

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

if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
@@ -207,12 +210,18 @@ static inline bool seccomp_check_mode(unsigned long seccomp_mode)
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;
- set_tsk_thread_flag(current, TIF_SECCOMP);
+ task->seccomp.mode = seccomp_mode;
+ /*
+ * 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
@@ -433,12 +442,17 @@ static int mode1_syscalls_32[] = {

int __secure_computing(int this_syscall)
{
- int mode = current->seccomp.mode;
int exit_sig = 0;
int *syscall;
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:
syscall = mode1_syscalls;
#ifdef CONFIG_COMPAT
@@ -543,7 +557,7 @@ static long seccomp_set_mode_strict(void)
#ifdef TIF_NOTSC
disable_TSC();
#endif
- seccomp_assign_mode(seccomp_mode);
+ seccomp_assign_mode(current, seccomp_mode);
ret = 0;

out:
@@ -593,7 +607,7 @@ static long seccomp_set_mode_filter(unsigned int flags,
/* Do not free the successfully attached filter. */
prepared = NULL;

- seccomp_assign_mode(seccomp_mode);
+ seccomp_assign_mode(current, seccomp_mode);
out:
spin_unlock_irq(&current->sighand->siglock);
seccomp_filter_free(prepared);
--
1.7.9.5


\
 
 \ /
  Last update: 2014-07-10 21:21    [W:0.136 / U:28.704 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site