curlx: curlx_strcopy() instead of strcpy()

This function REQUIRES the size of the target buffer as well as the
length of the source string. Meant to make it harder to do a bad
strcpy().

Removes 23 calls to strcpy().

Closes #20067

lib/curlx/curlx.h

@@ -55,6 +55,9 @@
 #include "strparse.h"
 /* The curlx_str_* parsing functions */
 
+#include "strcopy.h"
+/* curlx_strcopy */
+
 #include "dynbuf.h"
 /* The curlx_dyn_* functions */
 

lib/curlx/inet_ntop.c

@@ -33,6 +33,7 @@
 
 #include "inet_ntop.h"
 #include "snprintf.h"
+#include "strcopy.h"
 
 #define IN6ADDRSZ       16
 /* #define INADDRSZ         4 */
@@ -78,7 +79,7 @@ static char *inet_ntop4(const unsigned char *src, char *dst, size_t size)
 #endif
     return NULL;
   }
-  strcpy(dst, tmp);
+  curlx_strcopy(dst, size, tmp, len);
   return dst;
 }
 
@@ -183,8 +184,7 @@ static char *inet_ntop6(const unsigned char *src, char *dst, size_t size)
     *tp++ = ':';
   *tp++ = '\0';
 
-  /* Check for overflow, copy, and we are done.
-   */
+  /* Check for overflow, copy, and we are done. */
   if((size_t)(tp - tmp) > size) {
 #ifdef USE_WINSOCK
     errno = WSAEINVAL;
@@ -193,7 +193,8 @@ static char *inet_ntop6(const unsigned char *src, char *dst, size_t size)
 #endif
     return NULL;
   }
-  strcpy(dst, tmp);
+
+  curlx_strcopy(dst, size, tmp, strlen(tmp));
   return dst;
 }
 

lib/curlx/strcopy.c

@@ -0,0 +1,49 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ * SPDX-License-Identifier: curl
+ *
+ ***************************************************************************/
+#include "../curl_setup.h"
+#include "strcopy.h"
+
+/*
+ * curlx_strcopy() is a replacement for strcpy().
+ *
+ * Provide the target buffer @dest and size of the target buffer @dsize, If
+ * the source string @src with its *string length* @slen fits in the target
+ * buffer it will be copied there - including storing a null terminator.
+ *
+ * If the target buffer is too small, the copy is not performed but if the
+ * target buffer has a non-zero size it will get a null terminator stored.
+ */
+void curlx_strcopy(char *dest,      /* destination buffer */
+                   size_t dsize,    /* size of target buffer */
+                   const char *src, /* source string */
+                   size_t slen)     /* length of source string to copy */
+{
+  DEBUGASSERT(slen < dsize);
+  if(slen < dsize) {
+    memcpy(dest, src, slen);
+    dest[slen] = 0;
+  }
+  else if(dsize)
+    dest[0] = 0;
+}

lib/curlx/strcopy.h

@@ -0,0 +1,32 @@
+#ifndef HEADER_CURLX_STRCOPY_H
+#define HEADER_CURLX_STRCOPY_H
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ * SPDX-License-Identifier: curl
+ *
+ ***************************************************************************/
+
+void curlx_strcopy(char *dest,
+                   size_t dsize, /* size of target buffer */
+                   const char *src,
+                   size_t slen); /* length of string to copy */
+
+#endif /* HEADER_CURLX_STRCOPY_H */

lib/curlx/strerr.c

@@ -35,6 +35,7 @@
 #include "winapi.h"
 #include "snprintf.h"
 #include "strerr.h"
+#include "strcopy.h"
 
 #ifdef USE_WINSOCK
 /* This is a helper function for curlx_strerror that converts Winsock error
@@ -224,8 +225,7 @@ static const char *get_winsock_error(int err, char *buf, size_t len)
     return NULL;
   }
   alen = strlen(p);
-  if(alen < len)
-    strcpy(buf, p);
+  curlx_strcopy(buf, len, p, alen);
   return buf;
 #endif
 }

lib/curlx/winapi.c

@@ -30,6 +30,7 @@
 #ifdef _WIN32
 #include "winapi.h"
 #include "snprintf.h"
+#include "strcopy.h"
 
 /* This is a helper function for curlx_strerror that converts Windows API error
  * codes (GetLastError) to error messages.
@@ -93,8 +94,7 @@ const char *curlx_winapi_strerror(DWORD err, char *buf, size_t buflen)
 #else
   {
     const char *txt = (err == ERROR_SUCCESS) ? "No error" : "Error";
-    if(strlen(txt) < buflen)
-      strcpy(buf, txt);
+    curlx_strcopy(buf, buflen, txt, strlen(txt));
   }
 #endif