ftp: truncate command data that is too long

FTP control commands will be buffered forever until a new line is seen,
this can lead to memory exhaustion in Suricata.

To fix, set an upper bound, 4096 bytes on the size of the command that
is saved in the transaction. The input continues to be parsed to find
the end of the command so the parser can continue to move onto the next
command.

The result is that the command data in the transaction is truncated,
which also shows up in the ftp transaction logs.

This value is configurable with the max-line-length field in the ftp
app-layer.protocols section.

As FTP doesn't have events at this time, add a new fields to eve-log
that specificy if the request, or the response has been truncated.

Ticket #5024

diff --git a/src/app-layer-ftp.c b/src/app-layer-ftp.c
index 41548ee90a9030daccb337cbd05b6298c80d348c..b7ca50e771899d521cf8bb56ac40991e86f6b2c8 100644 (file)
--- a/src/app-layer-ftp.c
+++ b/src/app-layer-ftp.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 2007-2020 Open Information Security Foundation
+/* Copyright (C) 2007-2022 Open Information Security Foundation
  *
  * You can copy, redistribute or modify this Program under the terms of
  * the GNU General Public License version 2 as published by the Free
@@ -57,6 +57,7 @@
 #include "util-memrchr.h"
 #include "util-mem.h"
 #include "util-misc.h"
+#include "util-validate.h"
 
 #include "output-json.h"
 #include "rust.h"
@@ -126,6 +127,7 @@ const FtpCommand FtpCommands[FTP_COMMAND_MAX + 1] = {
 };
 uint64_t ftp_config_memcap = 0;
 uint32_t ftp_config_maxtx = 1024;
+uint32_t ftp_max_line_len = 4096;
 
 SC_ATOMIC_DECLARE(uint64_t, ftp_memuse);
 SC_ATOMIC_DECLARE(uint64_t, ftp_memcap);
@@ -163,6 +165,14 @@ static void FTPParseMemcap(void)
         }
         SCLogInfo("FTP max tx: %" PRIu32, ftp_config_maxtx);
     }
+
+    if ((ConfGet("app-layer.protocols.ftp.max-line-length", &conf_val)) == 1) {
+        if (ParseSizeStringU32(conf_val, &ftp_max_line_len) < 0) {
+            SCLogError(SC_ERR_SIZE_PARSE, "Error parsing ftp.max-line-length from conf file - %s.",
+                    conf_val);
+        }
+        SCLogConfig("FTP max line length: %" PRIu32, ftp_max_line_len);
+    }
 }
 
 static void FTPIncrMemuse(uint64_t size)
@@ -366,6 +376,7 @@ static int FTPGetLineForDirection(FtpState *state, FtpLineState *line_state)
         /* we have seen the lf for the previous line.  Clear the parser
          * details to parse new line */
         line_state->current_line_lf_seen = 0;
+        state->current_line_truncated = false;
         if (line_state->current_line_db == 1) {
             line_state->current_line_db = 0;
             FTPFree(line_state->db, line_state->db_len);
@@ -393,20 +404,27 @@ static int FTPGetLineForDirection(FtpState *state, FtpLineState *line_state)
             line_state->current_line_db = 1;
             memcpy(line_state->db, state->input, state->input_len);
             line_state->db_len = state->input_len;
-        } else {
-            ptmp = FTPRealloc(line_state->db, line_state->db_len,
-                             (line_state->db_len + state->input_len));
-            if (ptmp == NULL) {
-                FTPFree(line_state->db, line_state->db_len);
-                line_state->db = NULL;
-                line_state->db_len = 0;
-                return -1;
+        } else if (!state->current_line_truncated) {
+            int32_t input_len = state->input_len;
+            if (line_state->db_len + input_len > ftp_max_line_len) {
+                input_len = ftp_max_line_len - line_state->db_len;
+                DEBUG_VALIDATE_BUG_ON(input_len < 0);
+                state->current_line_truncated = true;
             }
-            line_state->db = ptmp;
+            if (input_len > 0) {
+                ptmp = FTPRealloc(
+                        line_state->db, line_state->db_len, (line_state->db_len + input_len));
+                if (ptmp == NULL) {
+                    FTPFree(line_state->db, line_state->db_len);
+                    line_state->db = NULL;
+                    line_state->db_len = 0;
+                    return -1;
+                }
+                line_state->db = ptmp;
 
-            memcpy(line_state->db + line_state->db_len,
-                   state->input, state->input_len);
-            line_state->db_len += state->input_len;
+                memcpy(line_state->db + line_state->db_len, state->input, input_len);
+                line_state->db_len += input_len;
+            }
         }
         state->input += state->input_len;
         state->input_len = 0;
@@ -417,27 +435,35 @@ static int FTPGetLineForDirection(FtpState *state, FtpLineState *line_state)
         line_state->current_line_lf_seen = 1;
 
         if (line_state->current_line_db == 1) {
-            ptmp = FTPRealloc(line_state->db, line_state->db_len,
-                             (line_state->db_len + (lf_idx + 1 - state->input)));
-            if (ptmp == NULL) {
-                FTPFree(line_state->db, line_state->db_len);
-                line_state->db = NULL;
-                line_state->db_len = 0;
-                return -1;
-            }
-            line_state->db = ptmp;
+            if (!state->current_line_truncated) {
+                int32_t input_len = lf_idx + 1 - state->input;
+                if (line_state->db_len + input_len > ftp_max_line_len) {
+                    input_len = ftp_max_line_len - line_state->db_len;
+                    DEBUG_VALIDATE_BUG_ON(input_len < 0);
+                    state->current_line_truncated = true;
+                }
+                if (input_len > 0) {
+                    ptmp = FTPRealloc(
+                            line_state->db, line_state->db_len, (line_state->db_len + input_len));
+                    if (ptmp == NULL) {
+                        FTPFree(line_state->db, line_state->db_len);
+                        line_state->db = NULL;
+                        line_state->db_len = 0;
+                        return -1;
+                    }
+                    line_state->db = ptmp;
 
-            memcpy(line_state->db + line_state->db_len,
-                   state->input, (lf_idx + 1 - state->input));
-            line_state->db_len += (lf_idx + 1 - state->input);
+                    memcpy(line_state->db + line_state->db_len, state->input, input_len);
+                    line_state->db_len += input_len;
 
-            if (line_state->db_len > 1 &&
-                line_state->db[line_state->db_len - 2] == 0x0D) {
-                line_state->db_len -= 2;
-                state->current_line_delimiter_len = 2;
-            } else {
-                line_state->db_len -= 1;
-                state->current_line_delimiter_len = 1;
+                    if (line_state->db_len > 1 && line_state->db[line_state->db_len - 2] == 0x0D) {
+                        line_state->db_len -= 2;
+                        state->current_line_delimiter_len = 2;
+                    } else {
+                        line_state->db_len -= 1;
+                        state->current_line_delimiter_len = 1;
+                    }
+                }
             }
 
             state->current_line = line_state->db;
@@ -445,7 +471,12 @@ static int FTPGetLineForDirection(FtpState *state, FtpLineState *line_state)
 
         } else {
             state->current_line = state->input;
-            state->current_line_len = lf_idx - state->input;
+            if (lf_idx - state->input > ftp_max_line_len) {
+                state->current_line_len = ftp_max_line_len;
+                state->current_line_truncated = true;
+            } else {
+                state->current_line_len = lf_idx - state->input;
+            }
 
             if (state->input != lf_idx &&
                 *(lf_idx - 1) == 0x0D) {
@@ -605,6 +636,7 @@ static AppLayerResult FTPParseRequest(Flow *f, void *ftp_state, AppLayerParserSt
         tx->command_descriptor = cmd_descriptor;
         tx->request_length = CopyCommandLine(&tx->request,
                 state->current_line, state->current_line_len);
+        tx->request_truncated = state->current_line_truncated;
 
         /* change direction (default to server) so expectation will handle
          * the correct message when expectation will match.
@@ -832,6 +864,7 @@ static AppLayerResult FTPParseResponse(Flow *f, void *ftp_state, AppLayerParserS
             FTPString *response = FTPStringAlloc();
             if (likely(response)) {
                 response->len = CopyCommandLine(&response->str, state->current_line, state->current_line_len);
+                response->truncated = state->current_line_truncated;
                 TAILQ_INSERT_TAIL(&tx->response_list, response, next);
             }
         }

diff --git a/src/app-layer-ftp.h b/src/app-layer-ftp.h
index 7232268055b883d9a0fb0b6539963b7909e54b64..09762c58486a4c0ad09bf3e78c64d5d0c3a63765 100644 (file)
--- a/src/app-layer-ftp.h
+++ b/src/app-layer-ftp.h
@@ -121,13 +121,14 @@ typedef struct FtpLineState_ {
     uint8_t *db;
     uint32_t db_len;
     uint8_t current_line_db;
-    /** we have see LF for the currently parsed line */
+    /** we have seen LF for the currently parsed line */
     uint8_t current_line_lf_seen;
 } FtpLineState;
 
 typedef struct FTPString_ {
     uint8_t *str;
     uint32_t len;
+    bool truncated;
     TAILQ_ENTRY(FTPString_) next;
 } FTPString;
 
@@ -140,6 +141,7 @@ typedef struct FTPTransaction_  {
     /* for the request */
     uint32_t request_length;
     uint8_t *request;
+    bool request_truncated;
 
     /* for the command description */
     const FtpCommand *command_descriptor;
@@ -173,6 +175,7 @@ typedef struct FtpState_ {
     /** length of the line in current_line.  Doesn't include the delimiter */
     uint32_t current_line_len;
     uint8_t current_line_delimiter_len;
+    bool current_line_truncated;
 
     /* 0 for toserver, 1 for toclient */
     FtpLineState line_state[2];

diff --git a/src/output-json-ftp.c b/src/output-json-ftp.c
index eae7d9ebbcb7bd83cda0c3481ac18aefb87b47b8..f4fd6fd4f727543a6b560ee5c9a2ad00d7575f52 100644 (file)
--- a/src/output-json-ftp.c
+++ b/src/output-json-ftp.c
@@ -66,8 +66,15 @@ static void EveFTPLogCommand(Flow *f, FTPTransaction *tx, JsonBuilder *jb)
                 "command_data",
                 (const uint8_t *)tx->request + min_length,
                 tx->request_length - min_length - 1);
+        if (tx->request_truncated) {
+            JB_SET_TRUE(jb, "command_truncated");
+        } else {
+            JB_SET_FALSE(jb, "command_truncated");
+        }
     }
 
+    bool reply_truncated = false;
+
     if (!TAILQ_EMPTY(&tx->response_list)) {
         int resp_code_cnt = 0;
         int resp_cnt = 0;
@@ -83,6 +90,9 @@ static void EveFTPLogCommand(Flow *f, FTPTransaction *tx, JsonBuilder *jb)
             } else if (response->len > UINT16_MAX) {
                 length = UINT16_MAX;
             }
+            if (!reply_truncated && response->truncated) {
+                reply_truncated = true;
+            }
             while ((pos = JsonGetNextLineFromBuffer((const char *)where, length)) != UINT16_MAX) {
                 uint16_t offset = 0;
                 /* Try to find a completion code for this line */
@@ -137,6 +147,12 @@ static void EveFTPLogCommand(Flow *f, FTPTransaction *tx, JsonBuilder *jb)
     } else {
         JB_SET_STRING(jb, "reply_received", "no");
     }
+
+    if (reply_truncated) {
+        JB_SET_TRUE(jb, "reply_truncated");
+    } else {
+        JB_SET_FALSE(jb, "reply_truncated");
+    }
 }