From 12d25272764bf2f9f828d5d129ec26622baf75eb Mon Sep 17 00:00:00 2001
From: MaxHearnden <maxoscarhearnden@gmail.com>
Date: Sun, 9 Feb 2025 20:53:58 +0000
Subject: [PATCH] Set FD_CLOEXEC on sockets created by curl

Curl creates sockets without setting FD_CLOEXEC/SOCK_CLOEXEC, this can
cause connections to remain open forever when using commands like `nix
shell`

This change sets the FD_CLOEXEC flag using a CURLOPT_SOCKOPTFUNCTION
callback.
---
 doc/manual/rl-next/curl-cloexec.md | 10 ++++++++++
 src/libstore/filetransfer.cc       | 12 ++++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 doc/manual/rl-next/curl-cloexec.md

diff --git a/doc/manual/rl-next/curl-cloexec.md b/doc/manual/rl-next/curl-cloexec.md
new file mode 100644
index 000000000..2fcdfb0d1
--- /dev/null
+++ b/doc/manual/rl-next/curl-cloexec.md
@@ -0,0 +1,10 @@
+---
+synopsis: Set FD_CLOEXEC on sockets created by curl
+issues: []
+prs: [12439]
+---
+
+
+Curl creates sockets without setting FD_CLOEXEC/SOCK_CLOEXEC, this can cause connections to remain open forever when using commands like `nix shell`
+
+This change sets the FD_CLOEXEC flag using a CURLOPT_SOCKOPTFUNCTION callback.
diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 8439cc39c..932e1d756 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -300,6 +300,14 @@ struct curlFileTransfer : public FileTransfer
             return ((TransferItem *) userp)->readCallback(buffer, size, nitems);
         }
 
+        #if !defined(_WIN32) && LIBCURL_VERSION_NUM >= 0x071000
+        static int cloexec_callback(void *, curl_socket_t curlfd, curlsocktype purpose) {
+            unix::closeOnExec(curlfd);
+            vomit("cloexec set for fd %i", curlfd);
+            return CURL_SOCKOPT_OK;
+        }
+        #endif
+
         void init()
         {
             if (!req) req = curl_easy_init();
@@ -359,6 +367,10 @@ struct curlFileTransfer : public FileTransfer
                 curl_easy_setopt(req, CURLOPT_SSL_VERIFYHOST, 0);
             }
 
+            #if !defined(_WIN32) && LIBCURL_VERSION_NUM >= 0x071000
+            curl_easy_setopt(req, CURLOPT_SOCKOPTFUNCTION, cloexec_callback);
+            #endif
+
             curl_easy_setopt(req, CURLOPT_CONNECTTIMEOUT, fileTransferSettings.connectTimeout.get());
 
             curl_easy_setopt(req, CURLOPT_LOW_SPEED_LIMIT, 1L);