swf: validate configured depth limits

SWF depth settings were previously limited only to values representable by
uint32_t. This is not sufficient for the buffer-size calculations performed
during SWF decompression.

The decompressed output requires an additional 8-byte FWS header. The
inspection buffer also grows by doubling a uint32_t size, so a required buffer
larger than 2 GiB can cause the growth calculation to wrap.

For LZMA input, a synthesized 13-byte header to the compressed
data is used. The configured compressed-data limit must leave room for this header.

This patch applies the following upper limits:

- decompress-depth: 2147483640 bytes
  (2 GiB minus the 8-byte FWS header)
- compress-depth: 4294967282 bytes
  (UINT32_MAX minus the 13-byte LZMA header

Ticket: #8914

doc/userguide/configuration/suricata-yaml.rst

@@ -1729,11 +1729,11 @@ use of libhtp.
        # 2 types: 'deflate', 'lzma', 'both' will decompress deflate and lzma
        # compress-depth:
        # Specifies the maximum amount of data to decompress,
-       # set 0 for unlimited.
+       # set 0 for unlimited. The maximum is 4294967282 bytes.
        # decompress-depth:
        # Specifies the maximum amount of decompressed data to obtain. The
        # output buffer grows on demand up to this limit. Set 0 to use the
-       # default limit of 50 MB.
+       # default limit of 50 MB. The maximum is 2147483640 bytes.
            swf-decompression:
              enabled: yes
              type: both

doc/userguide/rules/http-keywords.rst

@@ -872,11 +872,11 @@ setting.
     # 2 types: 'deflate', 'lzma', 'both' will decompress deflate and lzma
     # compress-depth:
     # Specifies the maximum amount of data to decompress,
-    # set 0 for unlimited.
+    # set 0 for unlimited. The maximum is 4294967282 bytes.
     # decompress-depth:
     # Specifies the maximum amount of decompressed data to obtain. The
     # output buffer grows on demand up to this limit. Set 0 to use the
-    # default limit of 50 MB.
+    # default limit of 50 MB. The maximum is 2147483640 bytes.
     swf-decompression:
       enabled: yes
       type: both

src/app-layer-htp.c

@@ -58,6 +58,7 @@
 #include "app-layer-events.h"
 
 #include "util-debug.h"
+#include "util-file-decompression.h"
 #include "util-misc.h"
 
 #include "util-unittest.h"
@@ -2336,17 +2337,19 @@ static void HTPConfigParseParameters(HTPCfgRec *cfg_prec, SCConfNode *s, struct
                         exit(EXIT_FAILURE);
                     }
                 } else if (strcasecmp("compress-depth", pval->name) == 0) {
-                    if (ParseSizeStringU32(pval->val, &cfg_prec->swf_compress_depth) < 0) {
-                        SCLogError("Error parsing swf-decompression.compression-depth "
-                                   "from conf file - %s. Killing engine",
-                                p->val);
+                    if (ParseSizeStringU32(pval->val, &cfg_prec->swf_compress_depth) < 0 ||
+                            cfg_prec->swf_compress_depth > MAX_SWF_COMPRESS_DEPTH) {
+                        SCLogError("Invalid swf-decompression.compress-depth value %s: the "
+                                   "maximum is %u bytes. Killing engine",
+                                pval->val, MAX_SWF_COMPRESS_DEPTH);
                         exit(EXIT_FAILURE);
                     }
                 } else if (strcasecmp("decompress-depth", pval->name) == 0) {
-                    if (ParseSizeStringU32(pval->val, &cfg_prec->swf_decompress_depth) < 0) {
-                        SCLogError("Error parsing swf-decompression.decompression-depth "
-                                   "from conf file - %s. Killing engine",
-                                p->val);
+                    if (ParseSizeStringU32(pval->val, &cfg_prec->swf_decompress_depth) < 0 ||
+                            cfg_prec->swf_decompress_depth > MAX_SWF_DECOMPRESS_DEPTH) {
+                        SCLogError("Invalid swf-decompression.decompress-depth value %s: the "
+                                   "maximum is %u bytes. Killing engine",
+                                pval->val, MAX_SWF_DECOMPRESS_DEPTH);
                         exit(EXIT_FAILURE);
                     }
                 } else {

src/tests/detect-file-data.c

@@ -349,6 +349,30 @@ static int DetectFiledataSwfDecompressDepthTest02(void)
     PASS;
 }
 
+/**
+ * \test SWF decompression rejects depth values above the supported limits.
+ */
+static int DetectFiledataSwfDecompressDepthTest03(void)
+{
+    DetectEngineThreadCtx *det_ctx = SCCalloc(1, sizeof(*det_ctx));
+    FAIL_IF_NULL(det_ctx);
+    InspectionBuffer out_buffer = { 0 };
+
+    int r = FileSwfDecompression(swf_lzma_fixture, (uint32_t)sizeof(swf_lzma_fixture), det_ctx,
+            &out_buffer, HTTP_SWF_COMPRESSION_LZMA, MAX_SWF_DECOMPRESS_DEPTH + 1, 0);
+    FAIL_IF(r != 0);
+    FAIL_IF_NOT_NULL(out_buffer.buf);
+
+    r = FileSwfDecompression(swf_lzma_fixture, (uint32_t)sizeof(swf_lzma_fixture), det_ctx,
+            &out_buffer, HTTP_SWF_COMPRESSION_LZMA, 0, MAX_SWF_COMPRESS_DEPTH + 1);
+    FAIL_IF(r != 0);
+    FAIL_IF_NOT_NULL(out_buffer.buf);
+
+    SCAppLayerDecoderEventsFreeEvents(&det_ctx->decoder_events);
+    SCFree(det_ctx);
+    PASS;
+}
+
 static int DetectEngineSMTPFiledataTest02(void)
 {
     DetectEngineCtx *de_ctx = DetectEngineCtxInit();
@@ -401,6 +425,8 @@ void DetectFiledataRegisterTests(void)
             "DetectFiledataSwfDecompressDepthTest01", DetectFiledataSwfDecompressDepthTest01);
     UtRegisterTest(
             "DetectFiledataSwfDecompressDepthTest02", DetectFiledataSwfDecompressDepthTest02);
+    UtRegisterTest(
+            "DetectFiledataSwfDecompressDepthTest03", DetectFiledataSwfDecompressDepthTest03);
     UtRegisterTest("DetectEngineSMTPFiledataTest02", DetectEngineSMTPFiledataTest02);
     UtRegisterTest("DetectFiledataParseTest04", DetectFiledataParseTest04);
 }

src/util-file-decompression.c

@@ -77,6 +77,10 @@ int FileSwfDecompression(const uint8_t *buffer, uint32_t buffer_len,
 {
     int r = 0;
 
+    if (decompress_depth > MAX_SWF_DECOMPRESS_DEPTH || compress_depth > MAX_SWF_COMPRESS_DEPTH) {
+        return 0;
+    }
+
     int compression_type = FileIsSwfFile(buffer, buffer_len);
     if (compression_type == FILE_SWF_NO_COMPRESSION) {
         return 0;
@@ -160,7 +164,7 @@ int FileSwfDecompression(const uint8_t *buffer, uint32_t buffer_len,
          * | 5 bytes         | 8 bytes             | n bytes         |
          * | LZMA properties | Uncompressed length | Compressed data |
          */
-        compressed_data_len += 13;
+        compressed_data_len += SWF_LZMA_HEADER_LEN;
         uint8_t *compressed_data = SCCalloc(1, compressed_data_len);
         if (compressed_data == NULL) {
             DetectEngineSetEvent(det_ctx, FILE_DECODER_EVENT_NO_MEM);
@@ -171,7 +175,8 @@ int FileSwfDecompression(const uint8_t *buffer, uint32_t buffer_len,
         /* put lzma end marker */
         memset(compressed_data + 5, 0xFF, 8);
         /* put compressed data */
-        memcpy(compressed_data + 13, buffer + offset, compressed_data_len - 13);
+        memcpy(compressed_data + SWF_LZMA_HEADER_LEN, buffer + offset,
+                compressed_data_len - SWF_LZMA_HEADER_LEN);
 
         /* the first 8 bytes represents the fws header, see 'FWS format' above.
          * data will start from 8th bytes

src/util-file-decompression.h

@@ -27,6 +27,12 @@
 
 #include "detect.h"
 
+#define SWF_HEADER_LEN      8
+#define SWF_LZMA_HEADER_LEN 13
+
+#define MAX_SWF_DECOMPRESS_DEPTH (UINT32_MAX / 2 + 1 - SWF_HEADER_LEN)
+#define MAX_SWF_COMPRESS_DEPTH   (UINT32_MAX - SWF_LZMA_HEADER_LEN)
+
 enum {
     FILE_IS_NOT_SWF = 0,
     FILE_SWF_NO_COMPRESSION,

src/util-file-swf-decompression.h

@@ -32,7 +32,6 @@
 
 #define MAX_SWF_DECOMPRESSED_LEN 50000000
 
-#define SWF_HEADER_LEN                    8
 #define SWF_DECOMPRESS_INITIAL_BUFFER_LEN 4096
 
 uint8_t FileGetSwfVersion(const uint8_t *buffer, const uint32_t buffer_len);

suricata.yaml.in

@@ -1172,10 +1172,11 @@ app-layer:
            # Two types: 'deflate', 'lzma', 'both' will decompress deflate and lzma
            # compress-depth:
            # Specifies the maximum amount of data to decompress,
-           # set 0 for unlimited.
+           # set 0 for unlimited. The maximum is 4294967282 bytes.
            # decompress-depth:
-           # Specifies the maximum amount of decompressed data to obtain,
-           # set 0 for unlimited.
+           # Specifies the maximum amount of decompressed data to obtain. The
+           # output buffer grows on demand up to this limit. Set 0 to use the
+           # default limit of 50 MB. The maximum is 2147483640 bytes.
            swf-decompression:
              enabled: no
              type: both