Be more strict about using invalid `pthread_t`s.
Another release, another attempt to remove the global thread list.
But this time, let's admit that it's not going away. We can switch to using
a read/write lock for the global thread list, and to aborting rather than
quietly returning ESRCH if we're given an invalid pthread_t.
This change affects pthread_detach, pthread_getcpuclockid,
pthread_getschedparam/pthread_setschedparam, pthread_join, and pthread_kill:
instead of returning ESRCH when passed an invalid pthread_t, if you're
targeting O or above, they'll abort with the message "attempt to use
invalid pthread_t".
Note that this doesn't change behavior as much as you might think: the old
lookup only held the global thread list lock for the duration of the lookup,
so there was still a race between that and the dereference in the caller,
given that callers actually need the tid to pass to some syscall or other,
and sometimes update fields in the pthread_internal_t struct too.
(This patch replaces such users with calls to pthread_gettid_np, which
at least makes the TOCTOU window smaller.)
We can't check thread->tid against 0 to see whether a pthread_t is still
valid because a dead thread gets its thread struct unmapped along with its
stack, so the dereference isn't safe.
Taking the affected functions one by one:
* pthread_getcpuclockid and pthread_getschedparam/pthread_setschedparam
should be fine. Unsafe calls to those seem highly unlikely.
* Unsafe pthread_detach callers probably want to switch to
pthread_attr_setdetachstate instead, or using
pthread_detach(pthread_self()) from the new thread's start routine
rather than doing the detach in the parent.
* pthread_join calls should be safe anyway, because a joinable thread
won't actually exit and unmap until it's joined. If you're joining an
unjoinable thread, the fix is to stop marking it detached. If you're
joining an already-joined thread, you need to rethink your design.
* Unsafe pthread_kill calls aren't portably fixable. (And are obviously
inherently non-portable as-is.) The best alternative on Android is to
use pthread_gettid_np at some point that you know the thread to be
alive, and then call kill/tgkill directly.
That's still not completely safe because if you're too late, the tid
may have been reused, but then your code is inherently unsafe anyway.
Bug: http://b/19636317
Test: ran tests
Change-Id: I0372c4428e8a7f1c3af5c9334f5d9c25f2c73f21
diff --git a/libc/bionic/pthread_getschedparam.cpp b/libc/bionic/pthread_getschedparam.cpp
index 052fb05..cc1ece8 100644
--- a/libc/bionic/pthread_getschedparam.cpp
+++ b/libc/bionic/pthread_getschedparam.cpp
@@ -34,15 +34,10 @@
int pthread_getschedparam(pthread_t t, int* policy, sched_param* param) {
ErrnoRestorer errno_restorer;
- pthread_internal_t* thread = __pthread_internal_find(t);
- if (thread == NULL) {
- return ESRCH;
- }
+ pid_t tid = pthread_gettid_np(t);
+ if (tid == -1) return ESRCH;
- int rc = sched_getparam(thread->tid, param);
- if (rc == -1) {
- return errno;
- }
- *policy = sched_getscheduler(thread->tid);
+ if (sched_getparam(tid, param) == -1) return errno;
+ *policy = sched_getscheduler(tid);
return 0;
}