ext/curl: error when curl read func returns unexpected long

Raise a value error when the callback registered with
CURLOPT_READFUNCTION returns an unexpected long.

The function registered with CURLOPT_READFUNCTION should return a
string. PHP then writes that string to a buffer and returns the
length, so that curl can read that many bytes from the buffer.

The function can also return CURL_READFUNC_ABORT and
CURL_READFUNC_PAUSE, so it also supports returning longs. However, when
it returns a long other than these two constants, it is interpreted as a
length. PHP does not update the buffer, but does instruct curl it can
read that many bytes from the buffer. It reads whatever uninitialized
data that is in the buffer and sends it over the line to the server.

This seems bad, so validate the return value of the read function and
raise an error.

Returning 0 is a bit of an edge case. It is not documented but does
results in correct behavior (i.e. end-of-file). So we accept that, but
don't advertise it as valid in the error message.

Related to #10270

Close GH-22757

Author: Sjord

NEWS

@@ -6,6 +6,10 @@ PHP                                                                        NEWS
   . Changed run-tests.php to run test subprocesses without a shell where
     possible. (NickSdot)
 
+- Curl:
+  . Raise a value error when the callback registered with CURLOPT_READFUNCTION
+    returns an unexpected long. (Sjoerd Langkemper)
+
 - Date:
   . Update timelib to 2026.01. (Derick, timwolla)
 

UPGRADING

@@ -24,6 +24,11 @@ PHP 8.6 UPGRADE NOTES
     has materialised the property by writing into the property table.
     The freshly-written value is returned directly. isset() is unaffected.
 
+- Curl:
+  . The callback registered with CURLOPT_READFUNCTION now throws a ValueError
+    when returning an integer other than 0, CURL_READFUNC_ABORT or
+    CURL_READFUNC_PAUSE.
+
 - COM
   . It is no longer possible to clone variant objects, this is because
     the cloning behaviour was ill defined.
@@ -602,6 +607,7 @@ PHP 8.6 UPGRADE NOTES
   . CURL_SEEKFUNC_OK.
   . CURL_SEEKFUNC_FAIL.
   . CURL_SEEKFUNC_CANTSEEK.
+  . CURL_READFUNC_ABORT.
 
 - OpenSSL:
   . OPENSSL_RSA_PSS_SALTLEN_DIGEST.

ext/curl/curl.stub.php

@@ -1788,6 +1788,11 @@
  * @cvalue CURLPAUSE_SEND_CONT
  */
 const CURLPAUSE_SEND_CONT = UNKNOWN;
+/**
+ * @var int
+ * @cvalue CURL_READFUNC_ABORT
+ */
+const CURL_READFUNC_ABORT = UNKNOWN;
 /**
  * @var int
  * @cvalue CURL_READFUNC_PAUSE

ext/curl/curl_arginfo.h

@@ -819,7 +819,13 @@ static size_t curl_read(char *data, size_t size, size_t nmemb, void *ctx)
 					length = MIN(nmemb, Z_STRLEN(retval));
 					memcpy(data, Z_STRVAL(retval), length);
 				} else if (Z_TYPE(retval) == IS_LONG) {
-					length = Z_LVAL_P(&retval);
+					zend_long long_rv = Z_LVAL_P(&retval);
+					if (long_rv == 0 || long_rv == CURL_READFUNC_ABORT || long_rv == CURL_READFUNC_PAUSE) {
+						length = (size_t) long_rv;
+					} else {
+						zend_value_error("The CURLOPT_READFUNCTION callback must return a string or CURL_READFUNC_ABORT or CURL_READFUNC_PAUSE");
+						length = CURL_READFUNC_ABORT;
+					}
 				}
 				// TODO Do type error if invalid type?
 				zval_ptr_dtor(&retval);

ext/curl/interface.c

@@ -0,0 +1,30 @@
+--TEST--
+error when CURLOPT_READFUNCTION returns an integer
+--EXTENSIONS--
+curl
+--FILE--
+<?php
+function custom_readfunction($oCurl, $hReadHandle, $iMaxOut)
+{
+    static $size = 2;
+    return $size--;
+}
+
+include 'server.inc';
+$host = curl_cli_server_start();
+$ch = curl_init();
+curl_setopt($ch, CURLOPT_URL, "{$host}/get.php?test=post");
+curl_setopt($ch, CURLOPT_POST, ['f' => 'f']);
+curl_setopt($ch, CURLOPT_TIMEOUT, 2);
+curl_setopt($ch, CURLOPT_READFUNCTION, "custom_readfunction" );
+
+try {
+    curl_exec($ch);
+} catch (ValueError $e) {
+    echo $e->getMessage() . "\n";
+}
+var_dump(curl_error($ch));
+?>
+--EXPECT--
+The CURLOPT_READFUNCTION callback must return a string or CURL_READFUNC_ABORT or CURL_READFUNC_PAUSE
+string(29) "operation aborted by callback"

ext/curl/tests/curl_read_function_error_on_int.phpt

@@ -0,0 +1,21 @@
+--TEST--
+Returning CURL_READFUNC_ABORT aborts the transfer
+--EXTENSIONS--
+curl
+--FILE--
+<?php
+include 'server.inc';
+$host = curl_cli_server_start();
+
+$ch = curl_init();
+curl_setopt($ch, CURLOPT_URL, "{$host}/get.inc");
+curl_setopt($ch, CURLOPT_POST, 1);
+curl_setopt($ch, CURLOPT_READFUNCTION, function () {
+	return CURL_READFUNC_ABORT;
+});
+curl_exec($ch);
+
+echo "No output expected, because transfer was aborted by read function.\n";
+?>
+--EXPECT--
+No output expected, because transfer was aborted by read function.