pthread_attr_get_np(): Use malloc(), report ENOMEM, don't tamper on error

Similarly as in the previous commit, using calloc() instead of malloc()
is useless here in the regular case since the subsequent call to
cpuset_getaffinify() is going to completely fill the allocated memory.

However, there is an additional complication.  This function tries to
allocate memory to hold the cpuset if it previously wasn't, and does so
before the thread lock is acquired, which can fail on a bad thread ID.
In this case, it is necessary to deallocate the memory allocated in this
function so that the attributes object appears unmodified to the caller
when an error is returned.  Without this, a subsequent call to
pthread_attr_getaffinity_np() would expose uninitialized memory (not
a security problem per se, since it comes from the same process) instead
of returning a full mask as it would before the failing call to
pthread_attr_get_np().  So the caller would be able to notice a change
in the state of the attributes object even if pthread_attr_get_np()
reported failure, which would be quite surprising.  A similar problem
that could occur on failure of cpuset_setaffinity() has been fixed.

Finally, we shall always report memory allocation failure.  This already
goes for pthread_attr_init(), so, if for nothing else, just be
consistent.

Reviewed by:            emaste, kib
Approved by:            emaste (mentor)
MFC after:              2 weeks
Sponsored by:           The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D43329

2 files changed, 27 insertions, 20 deletions

diff --git a/lib/libthr/thread/thr_attr.c b/lib/libthr/thread/thr_attr.c
index 561037fa5eb4..3c03225c33cb 100644
--- a/lib/libthr/thread/thr_attr.c
+++ b/lib/libthr/thread/thr_attr.c
@@ -129,8 +129,9 @@ __weak_reference(_thr_attr_get_np, _pthread_attr_get_np);
 int
 _thr_attr_get_np(pthread_t pthread, pthread_attr_t *dstattr)
 {
-	struct pthread_attr attr, *dst;
+	struct pthread_attr *dst;
 	struct pthread *curthread;
+	cpuset_t *cpuset;
 	size_t kern_size;
 	int error;
 
@@ -138,35 +139,43 @@ _thr_attr_get_np(pthread_t pthread, pthread_attr_t *dstattr)
 		return (EINVAL);
 
 	kern_size = _get_kern_cpuset_size();
-
 	if (dst->cpuset == NULL) {
-		dst->cpuset = calloc(1, kern_size);
-		dst->cpusetsize = kern_size;
-	}
+		if ((cpuset = malloc(kern_size)) == NULL)
+			return (ENOMEM);
+	} else
+		cpuset = dst->cpuset;
 
 	curthread = _get_curthread();
 	/* Arg 0 is to include dead threads. */
 	if ((error = _thr_find_thread(curthread, pthread, 0)) != 0)
-		return (error);
-
-	attr = pthread->attr;
-	if ((pthread->flags & THR_FLAGS_DETACHED) != 0)
-		attr.flags |= PTHREAD_DETACHED;
+		goto free_and_exit;
 
 	error = cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_TID, TID(pthread),
-	    dst->cpusetsize, dst->cpuset);
-	if (error == -1)
+	    kern_size, cpuset);
+	if (error == -1) {
+		THR_THREAD_UNLOCK(curthread, pthread);
 		error = errno;
+		goto free_and_exit;
+	}
 
-	THR_THREAD_UNLOCK(curthread, pthread);
+	/*
+	 * From this point on, we can't fail, so we can start modifying 'dst'.
+	 */
 
-	if (error == 0)
-		memcpy(&dst->pthread_attr_start_copy,
-		    &attr.pthread_attr_start_copy,
-		    offsetof(struct pthread_attr, pthread_attr_end_copy) -
-		    offsetof(struct pthread_attr, pthread_attr_start_copy));
+	*dst = pthread->attr;
+	if ((pthread->flags & THR_FLAGS_DETACHED) != 0)
+		dst->flags |= PTHREAD_DETACHED;
 
+	THR_THREAD_UNLOCK(curthread, pthread);
+
+	dst->cpuset = cpuset;
+	dst->cpusetsize = kern_size;
 	return (0);
+
+free_and_exit:
+	if (dst->cpuset == NULL)
+		free(cpuset);
+	return (error);
 }
 
 __weak_reference(_thr_attr_getdetachstate, pthread_attr_getdetachstate);
diff --git a/lib/libthr/thread/thr_private.h b/lib/libthr/thread/thr_private.h
index 3475029f8996..3fc4d02c611e 100644
--- a/lib/libthr/thread/thr_private.h
+++ b/lib/libthr/thread/thr_private.h
@@ -261,7 +261,6 @@ struct pthread_atfork {
 };
 
 struct pthread_attr {
-#define pthread_attr_start_copy	sched_policy
 	int	sched_policy;
 	int	sched_inherit;
 	int	prio;
@@ -271,7 +270,6 @@ struct pthread_attr {
 	void	*stackaddr_attr;
 	size_t	stacksize_attr;
 	size_t	guardsize_attr;
-#define pthread_attr_end_copy	cpuset
 	cpuset_t	*cpuset;
 	size_t	cpusetsize;
 };