Merge "clatd: rework buffer sizes" am: db02e4ef43

Original change: https://android-review.googlesource.com/c/platform/external/android-clat/+/2484896

Change-Id: I6138776fb4a31e18b5a66a747427dba313bb18b8
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

2 files changed, 14 insertions, 13 deletions

diff --git a/clatd.c b/clatd.c
index 98f5195..a089157 100644
--- a/clatd.c
+++ b/clatd.c
@@ -80,10 +80,10 @@ int ipv6_address_changed(const char *interface) {
 // reads L3 IPv6 packet from AF_PACKET socket, translates to IPv4, writes to tun
 void process_packet_6_to_4(struct tun_data *tunnel) {
   char cmsg_buf[CMSG_SPACE(sizeof(struct tpacket_auxdata))];
-  uint8_t buf[MAXMTU];
+  uint8_t buf[MAXMTU + 1];  // +1 to make packet truncation obvious
   struct iovec iov = {
     .iov_base = buf,
-    .iov_len = MAXMTU,
+    .iov_len = sizeof(buf),
   };
   struct msghdr msgh = {
     .msg_iov = &iov,
@@ -102,7 +102,7 @@ void process_packet_6_to_4(struct tun_data *tunnel) {
     logmsg(ANDROID_LOG_WARN, "%s: packet socket removed?", __func__);
     running = 0;
     return;
-  } else if (readlen >= MAXMTU) {
+  } else if (readlen >= sizeof(buf)) {
     logmsg(ANDROID_LOG_WARN, "%s: read truncation - ignoring pkt", __func__);
     return;
   }
@@ -131,8 +131,8 @@ void process_packet_6_to_4(struct tun_data *tunnel) {
 
 // reads TUN_PI + L3 IPv4 packet from tun, translates to IPv6, writes to AF_INET6/RAW socket
 void process_packet_4_to_6(struct tun_data *tunnel) {
-  uint8_t buf[PACKETLEN];
-  ssize_t readlen = read(tunnel->fd4, buf, PACKETLEN);
+  uint8_t buf[sizeof(struct tun_pi) + MAXMTU + 1]; // +1 to make packet truncation obvious
+  ssize_t readlen = read(tunnel->fd4, buf, sizeof(buf));
 
   if (readlen < 0) {
     if (errno != EAGAIN) {
@@ -143,7 +143,7 @@ void process_packet_4_to_6(struct tun_data *tunnel) {
     logmsg(ANDROID_LOG_WARN, "%s: tun interface removed", __func__);
     running = 0;
     return;
-  } else if (readlen >= PACKETLEN) {
+  } else if (readlen >= sizeof(buf)) {
     logmsg(ANDROID_LOG_WARN, "%s: read truncation - ignoring pkt", __func__);
     return;
   }
diff --git a/clatd.h b/clatd.h
index cfcb253..59f78ab 100644
--- a/clatd.h
+++ b/clatd.h
@@ -38,14 +38,15 @@ struct tun_data;
 //
 // (since there's no jumbogram support in IPv4, IPv6 jumbograms cannot be meaningfully
 // converted to IPv4 anyway, and are thus entirely unsupported)
-//
-// We bump it by one more, since it makes truncation more obvious.
-// ie. if we ever read >= MAXMTU bytes we should discard.
-#define MAXMTU (0xFFFF + 28 + 1)
-#define PACKETLEN (sizeof(struct tun_pi) + MAXMTU)
+#define MAXMTU (0xFFFF + 28)
 
-// logcat_hexdump() maximum binary data length
-#define MAXDUMPLEN PACKETLEN
+// logcat_hexdump() maximum binary data length, this is the maximum packet size
+// plus some extra space for various headers:
+//   struct tun_pi (4 bytes)
+//   struct virtio_net_hdr (10 bytes)
+//   ethernet (14 bytes), potentially including vlan tag (4) or tags (8 or 12)
+// plus some extra just-in-case headroom, because it doesn't hurt.
+#define MAXDUMPLEN (64 + MAXMTU)
 
 #define CLATD_VERSION "1.6"