Check that dest is valid for decompression

lib/decompress/zstd_decompress_block.c

@@ -2124,7 +2124,9 @@ ZSTD_decompressBlock_internal(ZSTD_DCtx* dctx,
         ip += seqHSize;
         srcSize -= seqHSize;
 
-        RETURN_ERROR_IF(dst == NULL && nbSeq > 0, dstSize_tooSmall, "NULL not handled");
+        RETURN_ERROR_IF((dst == NULL || dstCapacity == 0) && nbSeq > 0, dstSize_tooSmall, "NULL not handled");
+        RETURN_ERROR_IF(MEM_64bits() && sizeof(size_t) == sizeof(void*) && (size_t)(-1) - (size_t)dst < (size_t)(1 << 20), dstSize_tooSmall,
+                "invalid dst");
 
         /* If we could potentially have long offsets, or we might want to use the prefetch decoder,
          * compute information about the share of long offsets, and the maximum nbAdditionalBits.

tests/fuzz/block_decompress.c

@@ -13,6 +13,7 @@
  * decompression function to ensure the decompressor never crashes.
  */
 
+#include "fuzz_data_producer.h"
 #define ZSTD_STATIC_LINKING_ONLY
 
 #include <stddef.h>
@@ -28,11 +29,12 @@ static size_t bufSize = 0;
 int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
 {
     size_t const neededBufSize = ZSTD_BLOCKSIZE_MAX;
+    FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
 
     /* Allocate all buffers and contexts if not already allocated */
     if (neededBufSize > bufSize) {
         free(rBuf);
-        rBuf = FUZZ_malloc(neededBufSize);
+        rBuf = FUZZ_malloc_rand(neededBufSize, producer);
         bufSize = neededBufSize;
     }
     if (!dctx) {
@@ -42,6 +44,8 @@ int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
     ZSTD_decompressBegin(dctx);
     ZSTD_decompressBlock(dctx, rBuf, neededBufSize, src, size);
 
+    FUZZ_dataProducer_free(producer);
+
 #ifndef STATEFUL_FUZZING
     ZSTD_freeDCtx(dctx); dctx = NULL;
 #endif

tests/fuzz/fuzz_data_producer.c

@@ -8,6 +8,7 @@
  * You may select, at your option, one of the above-listed licenses.
  */
 
+#include "fuzz_helpers.h"
 #include "fuzz_data_producer.h"
 
 struct FUZZ_dataProducer_s{

tests/fuzz/fuzz_data_producer.h

@@ -24,7 +24,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-#include "fuzz_helpers.h"
 
 /* Struct used for maintaining the state of the data */
 typedef struct FUZZ_dataProducer_s FUZZ_dataProducer_t;

tests/fuzz/fuzz_helpers.c

@@ -23,6 +23,22 @@ void* FUZZ_malloc(size_t size)
     return NULL;
 }
 
+void* FUZZ_malloc_rand(size_t size, FUZZ_dataProducer_t *producer)
+{
+    if (size > 0) {
+        void* const mem = malloc(size);
+        FUZZ_ASSERT(mem);
+        return mem;
+    } else {
+        uintptr_t ptr = 0;
+        /* Add +- 1M 50% of the time */
+        if (FUZZ_dataProducer_uint32Range(producer, 0, 1))
+            FUZZ_dataProducer_int32Range(producer, -1000000, 1000000);
+        return (void*)ptr;
+    }
+
+}
+
 int FUZZ_memcmp(void const* lhs, void const* rhs, size_t size)
 {
     if (size == 0) {

tests/fuzz/fuzz_helpers.h

@@ -19,6 +19,7 @@
 #include "fuzz.h"
 #include "xxhash.h"
 #include "zstd.h"
+#include "fuzz_data_producer.h"
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -62,6 +63,12 @@ extern "C" {
  */
 void* FUZZ_malloc(size_t size);
 
+/**
+ * malloc except returns random pointer for zero sized data and FUZZ_ASSERT
+ * that malloc doesn't fail.
+ */
+void* FUZZ_malloc_rand(size_t size,  FUZZ_dataProducer_t *producer);
+
 /**
  * memcmp but accepts NULL.
  */