From 22b061b17679e1fc4886372790d2a25c9c7554ab Mon Sep 17 00:00:00 2001 From: Martijn Coenen Date: Fri, 26 May 2017 10:48:56 -0700 Subject: [PATCH] ANDROID: binder: don't check prio permissions on restore. 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 --- drivers/android/binder.c | 27 ++++++++++++++++++++------- 1 file changed, 20 insertions(+), 7 deletions(-) diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 8ce30dcef2ec..ec148be388b9 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -1108,8 +1108,9 @@ 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; @@ -1122,7 +1123,7 @@ 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) { @@ -1133,7 +1134,7 @@ 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) { @@ -1166,6 +1167,18 @@ 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, @@ -3236,7 +3249,7 @@ 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); @@ -3331,7 +3344,7 @@ err_invalid_target_handle: 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, @@ -3917,7 +3930,7 @@ retry: 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) { -- 2.20.1