Avoid expensive data copies for large packets, as for SFTP WRITE requ…

…ests, by implementing "direct read" accessors. (#1725)

contrib/mod_sftp/fxp.c

@@ -13263,7 +13263,7 @@ static int fxp_handle_write(struct fxp_packet *fxp) {
   name = sftp_msg_read_string(fxp->pool, &fxp->payload, &fxp->payload_sz);
   offset = sftp_msg_read_long(fxp->pool, &fxp->payload, &fxp->payload_sz);
   datalen = sftp_msg_read_int(fxp->pool, &fxp->payload, &fxp->payload_sz);
-  data = sftp_msg_read_data(fxp->pool, &fxp->payload, &fxp->payload_sz,
+  data = sftp_msg_read_data_direct(fxp->pool, &fxp->payload, &fxp->payload_sz,
     datalen);
 
   memset(cmd_arg, '\0', sizeof(cmd_arg));

contrib/mod_sftp/msg.c

@@ -1,6 +1,6 @@
 /*
  * ProFTPD - mod_sftp message format
- * Copyright (c) 2008-2022 TJ Saunders
+ * Copyright (c) 2008-2023 TJ Saunders
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -118,6 +118,24 @@ int sftp_msg_read_bool(pool *p, unsigned char **buf, uint32_t *buflen) {
 
 uint32_t sftp_msg_read_data2(pool *p, unsigned char **buf,
     uint32_t *buflen, size_t datalen, unsigned char **data) {
+  uint32_t len;
+
+  len = sftp_msg_read_data2_direct(p, buf, buflen, datalen, data);
+  if (len == 0) {
+    return 0;
+  }
+
+  *data = palloc(p, datalen);
+
+  memcpy(*data, *buf, datalen);
+  (*buf) += datalen;
+  (*buflen) -= datalen;
+
+  return datalen;
+}
+
+uint32_t sftp_msg_read_data2_direct(pool *p, unsigned char **buf,
+    uint32_t *buflen, size_t datalen, unsigned char **data) {
   if (datalen == 0) {
     return 0;
   }
@@ -129,12 +147,7 @@ uint32_t sftp_msg_read_data2(pool *p, unsigned char **buf,
     return 0;
   }
 
-  *data = palloc(p, datalen);
-
-  memcpy(*data, *buf, datalen);
-  (*buf) += datalen;
-  (*buflen) -= datalen;
-
+  *data = *buf;
   return datalen;
 }
 
@@ -160,6 +173,28 @@ unsigned char *sftp_msg_read_data(pool *p, unsigned char **buf,
   return data;
 }
 
+unsigned char *sftp_msg_read_data_direct(pool *p, unsigned char **buf,
+    uint32_t *buflen, size_t datalen) {
+  unsigned char *data = NULL;
+  uint32_t len;
+
+  if (datalen == 0) {
+    errno = EINVAL;
+    return NULL;
+  }
+
+  len = sftp_msg_read_data2_direct(p, buf, buflen, datalen, &data);
+  if (len == 0) {
+    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
+      "message format error: unable to read %lu bytes of raw data "
+      "(buflen = %lu)", (unsigned long) datalen, (unsigned long) *buflen);
+    pr_log_stacktrace(sftp_logfd, MOD_SFTP_VERSION);
+    SFTP_DISCONNECT_CONN(SFTP_SSH2_DISCONNECT_BY_APPLICATION, NULL);
+  }
+
+  return data;
+}
+
 uint32_t sftp_msg_read_int2(pool *p, unsigned char **buf, uint32_t *buflen,
     uint32_t *val) {
 

contrib/mod_sftp/msg.h

@@ -1,6 +1,6 @@
 /*
  * ProFTPD - mod_sftp message format
- * Copyright (c) 2008-2022 TJ Saunders
+ * Copyright (c) 2008-2023 TJ Saunders
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -30,6 +30,8 @@
 unsigned char sftp_msg_read_byte(pool *, unsigned char **, uint32_t *);
 int sftp_msg_read_bool(pool *, unsigned char **, uint32_t *);
 unsigned char *sftp_msg_read_data(pool *, unsigned char **, uint32_t *, size_t);
+unsigned char *sftp_msg_read_data_direct(pool *, unsigned char **, uint32_t *,
+  size_t);
 #if defined(PR_USE_OPENSSL_ECC)
 EC_POINT *sftp_msg_read_ecpoint(pool *, unsigned char **, uint32_t *,
   const EC_GROUP *, EC_POINT *);
@@ -46,6 +48,8 @@ char *sftp_msg_read_string(pool *, unsigned char **, uint32_t *);
 uint32_t sftp_msg_read_byte2(pool *, unsigned char **, uint32_t *, unsigned char *);
 uint32_t sftp_msg_read_bool2(pool *, unsigned char **, uint32_t *, int *);
 uint32_t sftp_msg_read_data2(pool *, unsigned char **, uint32_t *, size_t, unsigned char **);
+uint32_t sftp_msg_read_data2_direct(pool *, unsigned char **, uint32_t *,
+  size_t, unsigned char **);
 #if defined(PR_USE_OPENSSL_ECC)
 uint32_t sftp_msg_read_ecpoint2(pool *, unsigned char **, uint32_t *,
   const EC_GROUP *, EC_POINT **);