cpukit/libfs/jffs2: Prevent memory corruption due to corrupted data

The rtime decompression routine does not fully check bounds during the
entirety of the decompression pass and can corrupt memory outside the
decompression buffer if the compressed data is corrupted. This adds the
required check to prevent this failure mode.

Updates #5072

cpukit/libfs/src/jffs2/src/compr_rtime.c

@@ -113,6 +113,11 @@ int rtems_jffs2_compressor_rtime_decompress(
 
 		positions[value]=outpos;
 		if (repeat) {
+#ifdef __rtems__
+			if ((repeat + outpos) >= destlen) {
+				return 1;
+			}
+#endif
 			if (backoffs + repeat >= outpos) {
 				while(repeat) {
 					cpage_out[outpos++] = cpage_out[backoffs++];