Implement command GETNCNT for semctl.

PiperOrigin-RevId: 341154192

3 files changed, 48 insertions, 14 deletions

diff --git a/pkg/sentry/kernel/semaphore/semaphore.go b/pkg/sentry/kernel/semaphore/semaphore.go
index 310762936..b99c0bffa 100644
--- a/pkg/sentry/kernel/semaphore/semaphore.go
+++ b/pkg/sentry/kernel/semaphore/semaphore.go
@@ -103,6 +103,7 @@ type waiter struct {
 	waiterEntry
 
 	// value represents how much resource the waiter needs to wake up.
+	// The value is either 0 or negative.
 	value int16
 	ch    chan struct{}
 }
@@ -423,8 +424,7 @@ func (s *Set) GetPID(num int32, creds *auth.Credentials) (int32, error) {
 	return sem.pid, nil
 }
 
-// GetZeroWaiters returns number of waiters waiting for the sem to go to zero.
-func (s *Set) GetZeroWaiters(num int32, creds *auth.Credentials) (uint16, error) {
+func (s *Set) countWaiters(num int32, creds *auth.Credentials, pred func(w *waiter) bool) (uint16, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
@@ -437,13 +437,27 @@ func (s *Set) GetZeroWaiters(num int32, creds *auth.Credentials) (uint16, error)
 	if sem == nil {
 		return 0, syserror.ERANGE
 	}
-	var semzcnt uint16
+	var cnt uint16
 	for w := sem.waiters.Front(); w != nil; w = w.Next() {
-		if w.value == 0 {
-			semzcnt++
+		if pred(w) {
+			cnt++
 		}
 	}
-	return semzcnt, nil
+	return cnt, nil
+}
+
+// CountZeroWaiters returns number of waiters waiting for the sem's value to increase.
+func (s *Set) CountZeroWaiters(num int32, creds *auth.Credentials) (uint16, error) {
+	return s.countWaiters(num, creds, func(w *waiter) bool {
+		return w.value == 0
+	})
+}
+
+// CountNegativeWaiters returns number of waiters waiting for the sem to go to zero.
+func (s *Set) CountNegativeWaiters(num int32, creds *auth.Credentials) (uint16, error) {
+	return s.countWaiters(num, creds, func(w *waiter) bool {
+		return w.value < 0
+	})
 }
 
 // ExecuteOps attempts to execute a list of operations to the set. It only
@@ -598,11 +612,18 @@ func (s *Set) destroy() {
 	}
 }
 
+func abs(val int16) int16 {
+	if val < 0 {
+		return -val
+	}
+	return val
+}
+
 // wakeWaiters goes over all waiters and checks which of them can be notified.
 func (s *sem) wakeWaiters() {
 	// Note that this will release all waiters waiting for 0 too.
 	for w := s.waiters.Front(); w != nil; {
-		if s.value < w.value {
+		if s.value < abs(w.value) {
 			// Still blocked, skip it.
 			w = w.Next()
 			continue
diff --git a/pkg/sentry/syscalls/linux/linux64.go b/pkg/sentry/syscalls/linux/linux64.go
index 650ca16e6..bb1f715e2 100644
--- a/pkg/sentry/syscalls/linux/linux64.go
+++ b/pkg/sentry/syscalls/linux/linux64.go
@@ -118,7 +118,7 @@ var AMD64 = &kernel.SyscallTable{
 		63:  syscalls.Supported("uname", Uname),
 		64:  syscalls.Supported("semget", Semget),
 		65:  syscalls.PartiallySupported("semop", Semop, "Option SEM_UNDO not supported.", nil),
-		66:  syscalls.PartiallySupported("semctl", Semctl, "Options IPC_INFO, SEM_INFO, SEM_STAT, SEM_STAT_ANY, GETNCNT not supported.", nil),
+		66:  syscalls.PartiallySupported("semctl", Semctl, "Options IPC_INFO, SEM_INFO, SEM_STAT, SEM_STAT_ANY not supported.", nil),
 		67:  syscalls.Supported("shmdt", Shmdt),
 		68:  syscalls.ErrorWithEvent("msgget", syserror.ENOSYS, "", []string{"gvisor.dev/issue/135"}), // TODO(b/29354921)
 		69:  syscalls.ErrorWithEvent("msgsnd", syserror.ENOSYS, "", []string{"gvisor.dev/issue/135"}), // TODO(b/29354921)
@@ -619,7 +619,7 @@ var ARM64 = &kernel.SyscallTable{
 		188: syscalls.ErrorWithEvent("msgrcv", syserror.ENOSYS, "", []string{"gvisor.dev/issue/135"}),          // TODO(b/29354921)
 		189: syscalls.ErrorWithEvent("msgsnd", syserror.ENOSYS, "", []string{"gvisor.dev/issue/135"}),          // TODO(b/29354921)
 		190: syscalls.Supported("semget", Semget),
-		191: syscalls.PartiallySupported("semctl", Semctl, "Options IPC_INFO, SEM_INFO, SEM_STAT, SEM_STAT_ANY, GETNCNT not supported.", nil),
+		191: syscalls.PartiallySupported("semctl", Semctl, "Options IPC_INFO, SEM_INFO, SEM_STAT, SEM_STAT_ANY not supported.", nil),
 		192: syscalls.ErrorWithEvent("semtimedop", syserror.ENOSYS, "", []string{"gvisor.dev/issue/137"}),
 		193: syscalls.PartiallySupported("semop", Semop, "Option SEM_UNDO not supported.", nil),
 		194: syscalls.PartiallySupported("shmget", Shmget, "Option SHM_HUGETLB is not supported.", nil),
diff --git a/pkg/sentry/syscalls/linux/sys_sem.go b/pkg/sentry/syscalls/linux/sys_sem.go
index 067f6be6d..e383a0a87 100644
--- a/pkg/sentry/syscalls/linux/sys_sem.go
+++ b/pkg/sentry/syscalls/linux/sys_sem.go
@@ -139,14 +139,17 @@ func Semctl(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscal
 		return 0, nil, err
 
 	case linux.GETZCNT:
-		v, err := getSemzcnt(t, id, num)
+		v, err := getZCnt(t, id, num)
+		return uintptr(v), nil, err
+
+	case linux.GETNCNT:
+		v, err := getNCnt(t, id, num)
 		return uintptr(v), nil, err
 
 	case linux.IPC_INFO,
 		linux.SEM_INFO,
 		linux.SEM_STAT,
-		linux.SEM_STAT_ANY,
-		linux.GETNCNT:
+		linux.SEM_STAT_ANY:
 
 		t.Kernel().EmitUnimplementedEvent(t)
 		fallthrough
@@ -262,12 +265,22 @@ func getPID(t *kernel.Task, id int32, num int32) (int32, error) {
 	return int32(tg.ID()), nil
 }
 
-func getSemzcnt(t *kernel.Task, id int32, num int32) (uint16, error) {
+func getZCnt(t *kernel.Task, id int32, num int32) (uint16, error) {
+	r := t.IPCNamespace().SemaphoreRegistry()
+	set := r.FindByID(id)
+	if set == nil {
+		return 0, syserror.EINVAL
+	}
+	creds := auth.CredentialsFromContext(t)
+	return set.CountZeroWaiters(num, creds)
+}
+
+func getNCnt(t *kernel.Task, id int32, num int32) (uint16, error) {
 	r := t.IPCNamespace().SemaphoreRegistry()
 	set := r.FindByID(id)
 	if set == nil {
 		return 0, syserror.EINVAL
 	}
 	creds := auth.CredentialsFromContext(t)
-	return set.GetZeroWaiters(num, creds)
+	return set.CountNegativeWaiters(num, creds)
 }