3 files changed, 40 insertions, 4 deletions
diff --git a/pkg/sentry/kernel/semaphore/semaphore.go b/pkg/sentry/kernel/semaphore/semaphore.go
index c39ecfb8f..310762936 100644
--- a/pkg/sentry/kernel/semaphore/semaphore.go
+++ b/pkg/sentry/kernel/semaphore/semaphore.go
@@ -423,6 +423,29 @@ 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) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	// The calling process must have read permission on the semaphore set.
+	if !s.checkPerms(creds, fs.PermMask{Read: true}) {
+		return 0, syserror.EACCES
+	}
+
+	sem := s.findSem(num)
+	if sem == nil {
+		return 0, syserror.ERANGE
+	}
+	var semzcnt uint16
+	for w := sem.waiters.Front(); w != nil; w = w.Next() {
+		if w.value == 0 {
+			semzcnt++
+		}
+	}
+	return semzcnt, nil
+}
+
 // ExecuteOps attempts to execute a list of operations to the set. It only
 // succeeds when all operations can be applied. No changes are made if it fails.
 //
diff --git a/pkg/sentry/syscalls/linux/linux64.go b/pkg/sentry/syscalls/linux/linux64.go
index 36902d177..650ca16e6 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, GETZCNT not supported.", nil),
+		66:  syscalls.PartiallySupported("semctl", Semctl, "Options IPC_INFO, SEM_INFO, SEM_STAT, SEM_STAT_ANY, GETNCNT 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, GETZCNT not supported.", nil),
+		191: syscalls.PartiallySupported("semctl", Semctl, "Options IPC_INFO, SEM_INFO, SEM_STAT, SEM_STAT_ANY, GETNCNT 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 c2d4bf805..067f6be6d 100644
--- a/pkg/sentry/syscalls/linux/sys_sem.go
+++ b/pkg/sentry/syscalls/linux/sys_sem.go
@@ -138,12 +138,15 @@ func Semctl(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscal
 
 		return 0, nil, err
 
+	case linux.GETZCNT:
+		v, err := getSemzcnt(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.GETZCNT:
+		linux.GETNCNT:
 
 		t.Kernel().EmitUnimplementedEvent(t)
 		fallthrough
@@ -258,3 +261,13 @@ 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) {
+	r := t.IPCNamespace().SemaphoreRegistry()
+	set := r.FindByID(id)
+	if set == nil {
+		return 0, syserror.EINVAL
+	}
+	creds := auth.CredentialsFromContext(t)
+	return set.GetZeroWaiters(num, creds)
+}