Cap iovec array length in //pkg/sentry/hostfd.

PiperOrigin-RevId: 341001328

pkg/sentry/hostfd/BUILD

@@ -6,10 +6,12 @@ go_library(
     name = "hostfd",
     srcs = [
         "hostfd.go",
+        "hostfd_linux.go",
         "hostfd_unsafe.go",
     ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
+        "//pkg/log",
         "//pkg/safemem",
         "//pkg/sync",
         "@org_golang_x_sys//unix:go_default_library",

pkg/sentry/hostfd/hostfd_linux.go

@@ -0,0 +1,18 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hostfd
+
+// maxIov is the maximum permitted size of a struct iovec array.
+const maxIov = 1024 // UIO_MAXIOV

pkg/sentry/hostfd/hostfd_unsafe.go

@@ -20,6 +20,7 @@ import (
 	"unsafe"
 
 	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/safemem"
 )
 
@@ -44,6 +45,10 @@ func Preadv2(fd int32, dsts safemem.BlockSeq, offset int64, flags uint32) (uint6
 		}
 	} else {
 		iovs := safemem.IovecsFromBlockSeq(dsts)
+		if len(iovs) > maxIov {
+			log.Debugf("hostfd.Preadv2: truncating from %d iovecs to %d", len(iovs), maxIov)
+			iovs = iovs[:maxIov]
+		}
 		n, _, e = syscall.Syscall6(unix.SYS_PREADV2, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, uintptr(flags))
 	}
 	if e != 0 {
@@ -76,6 +81,10 @@ func Pwritev2(fd int32, srcs safemem.BlockSeq, offset int64, flags uint32) (uint
 		}
 	} else {
 		iovs := safemem.IovecsFromBlockSeq(srcs)
+		if len(iovs) > maxIov {
+			log.Debugf("hostfd.Preadv2: truncating from %d iovecs to %d", len(iovs), maxIov)
+			iovs = iovs[:maxIov]
+		}
 		n, _, e = syscall.Syscall6(unix.SYS_PWRITEV2, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, uintptr(flags))
 	}
 	if e != 0 {