Don't switch to using the packet mmap endpoint for zero length requests.

This matches linux's behavior. Reported-by: [email protected] Reported-by: [email protected] PiperOrigin-RevId: 724032784
google · Feb 6, 2025 · 213917f · 213917f
1 parent d8518f2
commit 213917f
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Showing 2 changed files with 31 additions and 3 deletions.
diff --git a/pkg/sentry/socket/netstack/netstack.go b/pkg/sentry/socket/netstack/netstack.go
@@ -2745,10 +2745,12 @@ func setSockOptPacket(t *kernel.Task, s socket.Socket, ep commonEndpoint, name i
 				pme = &packetmmap.Endpoint{}
 			}
 			opts := ep.GetPacketMMapOpts(&req, true /* isRx */)
-			if err := pme.Init(t, opts); err != nil {
-				return syserr.FromError(err)
+			if opts.Req.TpFrameNr != 0 || opts.Req.TpBlockNr != 0 {
+				if err := pme.Init(t, opts); err != nil {
+					return syserr.FromError(err)
+				}
+				ep.SetPacketMMapEndpoint(pme)
 			}
-			ep.SetPacketMMapEndpoint(pme)
 		} else {
 			return syserr.ErrNotSupported
 		}

diff --git a/test/syscalls/linux/packet_mmap.cc b/test/syscalls/linux/packet_mmap.cc
@@ -257,6 +257,32 @@ TEST(PacketMmapTest, FillBlocks) {
   EXPECT_STREQ((char*)(hdr) + hdr->tp_net, kNewMessage.c_str());
 }
 
+TEST(PacketMmapTest, ZeroSizeRing) {
+  if (!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_NET_RAW))) {
+    ASSERT_THAT(socket(AF_PACKET, SOCK_RAW, 0), SyscallFailsWithErrno(EPERM));
+    GTEST_SKIP() << "Missing packet socket capability";
+  }
+  sockaddr_ll bind_addr = {
+      .sll_family = AF_PACKET,
+      .sll_protocol = htons(ETH_P_IP),
+      .sll_ifindex = ASSERT_NO_ERRNO_AND_VALUE(GetLoopbackIndex()),
+      .sll_halen = ETH_ALEN,
+  };
+  FileDescriptor mmap_sock =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(AF_PACKET, SOCK_DGRAM, 0));
+
+  tpacket_req req = {};
+  ASSERT_NO_ERRNO_AND_VALUE(MakePacketMmapRing(
+      mmap_sock.get(), reinterpret_cast<const sockaddr*>(&bind_addr),
+      sizeof(bind_addr), &req));
+
+  std::string kMessage = "123abc";
+  ASSERT_THAT(
+      sendto(mmap_sock.get(), kMessage.c_str(), kMessage.size(), 0 /* flags */,
+             reinterpret_cast<const sockaddr*>(&bind_addr), sizeof(bind_addr)),
+      SyscallSucceeds());
+}
+
 TEST(PacketMmapTest, ConcurrentReadWrite) {
   if (!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_NET_RAW))) {
     ASSERT_THAT(socket(AF_PACKET, SOCK_RAW, 0), SyscallFailsWithErrno(EPERM));