The local task in process_vm_read|writev is just the calling task.

We were using t.ThreadGroup.Leader() as the local task, which led to data races
reading fields that are owned by the task goroutine. But there's no need to use
the Leader, so we just use the calling task everywhere.

PiperOrigin-RevId: 570826256

pkg/sentry/syscalls/linux/sys_process_vm.go

@@ -65,15 +65,10 @@ func processVMOp(t *kernel.Task, args arch.SyscallArguments, op processVMOpType)
 		return 0, nil, linuxerr.EFAULT
 	}
 
-	// Determine local and remote processes.
-	// Local process is always the caller.
-	localTask := t.ThreadGroup().Leader()
-	if localTask == nil {
-		return 0, nil, linuxerr.ESRCH
-	}
-	// Remote process is the pid specified in the syscall arguments. It is
-	// allowed to be the same as the caller process.
-	remoteThreadGroup := localTask.PIDNamespace().ThreadGroupWithID(pid)
+	// Local process is always the current task (t). Remote process is the
+	// pid specified in the syscall arguments. It is allowed to be the same
+	// as the caller process.
+	remoteThreadGroup := t.PIDNamespace().ThreadGroupWithID(pid)
 	if remoteThreadGroup == nil {
 		return 0, nil, linuxerr.ESRCH
 	}
@@ -85,7 +80,7 @@ func processVMOp(t *kernel.Task, args arch.SyscallArguments, op processVMOpType)
 	// man 2 process_vm_read: "Permission to read from or write to another
 	// process is governed by a ptrace access mode
 	// PTRACE_MODE_ATTACH_REALCREDS check; see ptrace(2)."
-	if !localTask.CanTrace(remoteTask, true /* attach */) {
+	if !t.CanTrace(remoteTask, true /* attach */) {
 		return 0, nil, linuxerr.EPERM
 	}
 
@@ -99,14 +94,14 @@ func processVMOp(t *kernel.Task, args arch.SyscallArguments, op processVMOpType)
 			readCtx:         remoteTask.CopyContext(t, usermem.IOOpts{}),
 			readAddr:        rvec,
 			readIovecCount:  riovcnt,
-			writeCtx:        localTask.CopyContext(t, usermem.IOOpts{AddressSpaceActive: true}),
+			writeCtx:        t.CopyContext(t, usermem.IOOpts{AddressSpaceActive: true}),
 			writeAddr:       lvec,
 			writeIovecCount: liovcnt,
 		}
 	case processVMOpWrite:
 		// Read from local process and write into remote.
 		opArgs = processVMOpArgs{
-			readCtx:         localTask.CopyContext(t, usermem.IOOpts{AddressSpaceActive: true}),
+			readCtx:         t.CopyContext(t, usermem.IOOpts{AddressSpaceActive: true}),
 			readAddr:        lvec,
 			readIovecCount:  liovcnt,
 			writeCtx:        remoteTask.CopyContext(t, usermem.IOOpts{}),
@@ -121,7 +116,7 @@ func processVMOp(t *kernel.Task, args arch.SyscallArguments, op processVMOpType)
 		n   int
 		err error
 	)
-	if localTask == remoteTask {
+	if t == remoteTask {
 		// No need to lock remote process's task mutex since it is the
 		// same as this process.
 		n, err = doProcessVMOpMaybeLocked(t, opArgs)