From deff138e7eb4b0f89ea390b26715a3e543e9bd12 Mon Sep 17 00:00:00 2001
From: Gavin Hayes <gavin@computoid.com>
Date: Fri, 3 May 2024 11:03:57 -0400
Subject: [PATCH] recvfrom: don't convert address if addrsize is 0 (#1153)

---
 libc/sock/recvfrom.c           | 13 ++++++++---
 test/libc/sock/recvfrom_test.c | 41 ++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/libc/sock/recvfrom.c b/libc/sock/recvfrom.c
index 98cd7317e..d3e326f1b 100644
--- a/libc/sock/recvfrom.c
+++ b/libc/sock/recvfrom.c
@@ -70,6 +70,9 @@ ssize_t recvfrom(int fd, void *buf, size_t size, int flags,
     if (__isfdkind(fd, kFdSocket)) {
       rc = sys_recvfrom_nt(fd, (struct iovec[]){{buf, size}}, 1, flags, &addr,
                            &addrsize);
+      if (rc != -1 && addrsize == sizeof(addr)) {
+        addrsize = 0;
+      }
     } else if (__isfdkind(fd, kFdFile) && !opt_out_srcaddr) { /* socketpair */
       if (!flags) {
         rc = sys_read_nt(fd, (struct iovec[]){{buf, size}}, 1, -1);
@@ -84,10 +87,14 @@ ssize_t recvfrom(int fd, void *buf, size_t size, int flags,
   }
 
   if (rc != -1) {
-    if (IsBsd()) {
-      __convert_bsd_to_sockaddr(&addr);
+    if (addrsize) {
+      if (IsBsd()) {
+        __convert_bsd_to_sockaddr(&addr);
+      }
+      __write_sockaddr(&addr, opt_out_srcaddr, opt_inout_srcaddrsize);
+    } else {
+      *opt_inout_srcaddrsize = 0;
     }
-    __write_sockaddr(&addr, opt_out_srcaddr, opt_inout_srcaddrsize);
   }
 
   END_CANCELATION_POINT;
diff --git a/test/libc/sock/recvfrom_test.c b/test/libc/sock/recvfrom_test.c
index 8126a8f4e..4ef3c7a11 100644
--- a/test/libc/sock/recvfrom_test.c
+++ b/test/libc/sock/recvfrom_test.c
@@ -93,3 +93,44 @@ TEST(recvfrom, test) {
   EXPECT_SYS(0, 0, close(client1));
   WAIT(exit, 0);
 }
+
+// server listens for connections, accepts a connection, and sends data
+// client connects to server recieves with recvfrom and verifies addrsize
+// is 0 as the sender info isn't available on connection sockets.
+TEST(recvfrom, tcp) {
+  uint32_t addrsize = sizeof(struct sockaddr_in);
+  struct sockaddr_in server = {
+      .sin_family = AF_INET,
+      .sin_addr.s_addr = htonl(0x7f000001),
+  };
+  ASSERT_SYS(0, 3, socket(AF_INET, SOCK_STREAM, IPPROTO_TCP));
+  ASSERT_SYS(0, 0, bind(3, (struct sockaddr *)&server, sizeof(server)));
+  ASSERT_SYS(0, 0, getsockname(3, (struct sockaddr *)&server, &addrsize));
+  ASSERT_SYS(0, 0, listen(3, 5));
+
+  ////////////////////////////////////////////////////////////////////////////////
+  SPAWN(fork);
+  struct sockaddr_in data, addr;
+  uint32_t addrsize = sizeof(struct sockaddr_in);
+  EXPECT_SYS(0, 0, close(3));
+  ASSERT_SYS(0, 3, socket(AF_INET, SOCK_STREAM, IPPROTO_TCP));
+  ASSERT_SYS(0, 0, connect(3, (struct sockaddr *)&server, sizeof(server)));
+  ASSERT_SYS(
+      0, sizeof(data),
+      recvfrom(3, &data, sizeof(data), 0, (struct sockaddr *)&addr, &addrsize));
+  ASSERT_EQ(0, addrsize);
+  EXPECT_SYS(0, 0, close(3));
+
+  ////////////////////////////////////////////////////////////////////////////////
+  PARENT();
+  int client;
+  struct sockaddr client_sockaddr;
+  uint32_t sockaddr_size = sizeof(client_sockaddr);
+  ASSERT_NE(-1, (client = accept(3, &client_sockaddr, &sockaddr_size)));
+  ASSERT_SYS(0, sizeof(client_sockaddr),
+             sendto(client, &client_sockaddr, sizeof(client_sockaddr), 0,
+                    (struct sockaddr *)&server, sizeof(server)));
+  EXPECT_SYS(0, 0, close(client));
+  WAIT(exit, 0);
+  EXPECT_SYS(0, 0, close(3));
+}