PDF: Fix error Attempt to allocate 0 bytes

The PDF parser currently prints verbose error messages when attempting
to shrink a buffer down to actual data length after decoding if it turns
out that the decoded stream was empty (0 bytes).  With exception to the
verbose error messages, there's no real behavior issue.

This commit fixes the issue by checking if any bytes were decoded before
attempting to shrink the buffer.

libclamav/pdfdecode.c

@@ -638,8 +638,11 @@ static cl_error_t filter_rldecode(struct pdf_struct *pdf, struct pdf_obj *obj, s
     }
 
     if (rc == CL_SUCCESS) {
-        /* Shrink output buffer to final the decoded data length to minimize RAM usage */
-        if (!(temp = cli_realloc(decoded, declen))) {
+        if (declen == 0) {
+            cli_dbgmsg("cli_pdf: empty stream after inflation completed.\n");
+            rc = CL_BREAK;
+        } else if (!(temp = cli_realloc(decoded, declen))) {
+            /* Shrink output buffer to final the decoded data length to minimize RAM usage */
             cli_errmsg("cli_pdf: cannot reallocate memory for decoded output\n");
             rc = CL_EMEM;
         } else {
@@ -647,7 +650,7 @@ static cl_error_t filter_rldecode(struct pdf_struct *pdf, struct pdf_obj *obj, s
         }
     }
 
-    if (rc == CL_SUCCESS) {
+    if (rc == CL_SUCCESS || rc == CL_BREAK) {
         free(token->content);
 
         cli_dbgmsg("cli_pdf: decoded %lu bytes from %lu total bytes\n",
@@ -817,8 +820,11 @@ static cl_error_t filter_flatedecode(struct pdf_struct *pdf, struct pdf_obj *obj
     (void)inflateEnd(&stream);
 
     if (rc == CL_SUCCESS) {
-        /* Shrink output buffer to final the decoded data length to minimize RAM usage */
-        if (!(temp = cli_realloc(decoded, declen))) {
+        if (declen == 0) {
+            cli_dbgmsg("cli_pdf: empty stream after inflation completed.\n");
+            rc = CL_BREAK;
+        } else if (!(temp = cli_realloc(decoded, declen))) {
+            /* Shrink output buffer to final the decoded data length to minimize RAM usage */
             cli_errmsg("cli_pdf: cannot reallocate memory for decoded output\n");
             rc = CL_EMEM;
         } else {
@@ -826,7 +832,7 @@ static cl_error_t filter_flatedecode(struct pdf_struct *pdf, struct pdf_obj *obj
         }
     }
 
-    if (rc == CL_SUCCESS) {
+    if (rc == CL_SUCCESS || rc == CL_BREAK) {
         free(token->content);
 
         token->content = decoded;
@@ -1099,8 +1105,11 @@ static cl_error_t filter_lzwdecode(struct pdf_struct *pdf, struct pdf_obj *obj,
     (void)lzwInflateEnd(&stream);
 
     if (rc == CL_SUCCESS) {
-        /* Shrink output buffer to final the decoded data length to minimize RAM usage */
-        if (!(temp = cli_realloc(decoded, declen))) {
+        if (declen == 0) {
+            cli_dbgmsg("cli_pdf: empty stream after inflation completed.\n");
+            rc = CL_BREAK;
+        } else if (!(temp = cli_realloc(decoded, declen))) {
+            /* Shrink output buffer to final the decoded data length to minimize RAM usage */
             cli_errmsg("cli_pdf: cannot reallocate memory for decoded output\n");
             rc = CL_EMEM;
         } else {
@@ -1108,7 +1117,7 @@ static cl_error_t filter_lzwdecode(struct pdf_struct *pdf, struct pdf_obj *obj,
         }
     }
 
-    if (rc == CL_SUCCESS) {
+    if (rc == CL_SUCCESS || rc == CL_BREAK) {
         free(token->content);
 
         token->content = decoded;