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ANDROID: binder: don't check prio permissions on restore.

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Because we have disabled RT priority inheritance for
the regular binder domain, the following can happen:

1) thread A (prio 98) calls into thread B
2) because RT prio inheritance is disabled, thread B
   runs at the lowest nice (prio 100) instead
3) thread B calls back into A; A will run at prio 100
   for the duration of the transaction
4) When thread A is done with the call from B, we will
   try to restore the prio back to 98. But, we fail
   because the process doesn't hold CAP_SYS_NICE,
   neither is RLIMIT_RT_PRIO set.

While the proper fix going forward will be to
correctly apply CAP_SYS_NICE or RLIMIT_RT_PRIO,
for now it seems reasonable to not check permissions
on the restore path.

Change-Id: Ibede5960c9b7bb786271c001e405de50be64d944
Signed-off-by: Martijn Coenen <maco@android.com>
This commit is contained in:
Martijn Coenen 2017-05-26 10:48:56 -07:00 committed by Amit Pundir
parent f27fca4659
commit eb220f5318
1 changed files with 20 additions and 7 deletions
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27
drivers/android/binder.c
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@ -1109,8 +1109,9 @@ static int to_kernel_prio(int policy, int user_priority)
return MAX_USER_RT_PRIO - 1 - user_priority;
}
static void binder_set_priority(struct task_struct *task,
struct binder_priority desired)
static void binder_do_set_priority(struct task_struct *task,
struct binder_priority desired,
bool verify)
{
int priority; /* user-space prio value */
bool has_cap_nice;
@ -1123,7 +1124,7 @@ static void binder_set_priority(struct task_struct *task,
priority = to_userspace_prio(policy, desired.prio);
if (is_rt_policy(policy) && !has_cap_nice) {
if (verify && is_rt_policy(policy) && !has_cap_nice) {
long max_rtprio = task_rlimit(task, RLIMIT_RTPRIO);
if (max_rtprio == 0) {
@ -1134,7 +1135,7 @@ static void binder_set_priority(struct task_struct *task,
}
}
if (is_fair_policy(policy) && !has_cap_nice) {
if (verify && is_fair_policy(policy) && !has_cap_nice) {
long min_nice = rlimit_to_nice(task_rlimit(task, RLIMIT_NICE));
if (min_nice > MAX_NICE) {
@ -1167,6 +1168,18 @@ static void binder_set_priority(struct task_struct *task,
set_user_nice(task, priority);
}
static void binder_set_priority(struct task_struct *task,
struct binder_priority desired)
{
binder_do_set_priority(task, desired, /* verify = */ true);
}
static void binder_restore_priority(struct task_struct *task,
struct binder_priority desired)
{
binder_do_set_priority(task, desired, /* verify = */ false);
}
static void binder_transaction_priority(struct task_struct *task,
struct binder_transaction *t,
struct binder_priority node_prio,
@ -3204,7 +3217,7 @@ static void binder_transaction(struct binder_proc *proc,
binder_enqueue_work_ilocked(&t->work, &target_thread->todo);
binder_inner_proc_unlock(target_proc);
wake_up_interruptible_sync(&target_thread->wait);
binder_set_priority(current, in_reply_to->saved_priority);
binder_restore_priority(current, in_reply_to->saved_priority);
binder_free_transaction(in_reply_to);
} else if (!(t->flags & TF_ONE_WAY)) {
BUG_ON(t->buffer->async_transaction != 0);
@ -3293,7 +3306,7 @@ static void binder_transaction(struct binder_proc *proc,
BUG_ON(thread->return_error.cmd != BR_OK);
if (in_reply_to) {
binder_set_priority(current, in_reply_to->saved_priority);
binder_restore_priority(current, in_reply_to->saved_priority);
thread->return_error.cmd = BR_TRANSACTION_COMPLETE;
binder_enqueue_work(thread->proc,
&thread->return_error.work,
@ -3893,7 +3906,7 @@ static int binder_thread_read(struct binder_proc *proc,
wait_event_interruptible(binder_user_error_wait,
binder_stop_on_user_error < 2);
}
binder_set_priority(current, proc->default_priority);
binder_restore_priority(current, proc->default_priority);
}
if (non_block) {