Reject Irregular Dictionary Files

I hadn't seen #2890, so I wrote my own version. I like this approach a little
better, since it does an explicit check for a regular file, rather than
passing a magic value.

Addresses #2874.

programs/fileio.c

@@ -732,22 +732,33 @@ static size_t FIO_createDictBuffer(void** bufferPtr, const char* fileName, FIO_p
 {
     FILE* fileHandle;
     U64 fileSize;
+    stat_t statbuf;
 
     assert(bufferPtr != NULL);
     *bufferPtr = NULL;
     if (fileName == NULL) return 0;
 
     DISPLAYLEVEL(4,"Loading %s as dictionary \n", fileName);
+
+    if (!UTIL_stat(fileName, &statbuf)) {
+        EXM_THROW(31, "Stat failed on dictionary file %s.", fileName);
+    }
+
+    if (!UTIL_isRegularFileStat(&statbuf)) {
+        EXM_THROW(32, "Dictionary %s must be a regular file.", fileName);
+    }
+
     fileHandle = fopen(fileName, "rb");
-    if (fileHandle==NULL) EXM_THROW(31, "%s: %s", fileName, strerror(errno));
 
-    fileSize = UTIL_getFileSize(fileName);
-    if (fileSize == UTIL_FILESIZE_UNKNOWN) 
-    	EXM_THROW(32, "This file format is not supported : Dictionary file %s\n", fileName);
+    if (fileHandle == NULL) {
+        EXM_THROW(33, "Couldn't open dictionary %s: %s", fileName, strerror(errno));
+    }
+
+    fileSize = UTIL_getFileSizeStat(&statbuf);
     {
         size_t const dictSizeMax = prefs->patchFromMode ? prefs->memLimit : DICTSIZE_MAX;
         if (fileSize >  dictSizeMax) {
-            EXM_THROW(32, "Dictionary file %s is too large (> %u bytes)",
+            EXM_THROW(34, "Dictionary file %s is too large (> %u bytes)",
                             fileName,  (unsigned)dictSizeMax);   /* avoid extreme cases */
         }
     }

tests/playTests.sh

@@ -974,6 +974,11 @@ println "- Dictionary compression with btlazy2 strategy"
 zstd -f tmp -D tmpDict --zstd=strategy=6
 zstd -d tmp.zst -D tmpDict -fo result
 $DIFF "$TESTFILE" result
+if [ -e /dev/stdin ]; then
+    println "- Test rejecting irregular dictionary file"
+    cat tmpDict | zstd -f tmp -D /dev/stdin 2>&1 | grep 'regular file' || die "Correct error message not detected!"
+    cat tmpDict | zstd -d tmp.zst -D /dev/stdin -f 2>&1 | grep 'regular file' || die "Correct error message not detected!"
+fi
 if [ -n "$hasMT" ]
 then
     println "- Test dictionary compression with multithreading "