diff --git a/net/lwip/tftp.c b/net/lwip/tftp.c
index 4f9b204..162c141 100644
--- a/net/lwip/tftp.c
+++ b/net/lwip/tftp.c
@@ -8,6 +8,7 @@
 #include <efi_loader.h>
 #include <image.h>
 #include <linux/delay.h>
+#include <linux/kconfig.h>
 #include <lwip/apps/tftp_client.h>
 #include <lwip/timeouts.h>
 #include <mapmem.h>
@@ -31,6 +32,47 @@
 	enum done_state done;
 };
 
+/**
+ * store_block() - copy received data
+ *
+ * This function is called by the receive callback to copy a block of data
+ * into its final location (ctx->daddr). Before doing so, it checks if the copy
+ * is allowed.
+ *
+ * @ctx: the context for the current transfer
+ * @src: the data received from the TCP stack
+ * @len: the length of the data
+ */
+static int store_block(struct tftp_ctx *ctx, void *src, u16_t len)
+{
+	ulong store_addr = ctx->daddr;
+	void *ptr;
+
+	if (CONFIG_IS_ENABLED(LMB)) {
+		if (store_addr + len < store_addr ||
+		    lmb_read_check(store_addr, len)) {
+			puts("\nTFTP error: ");
+			puts("trying to overwrite reserved memory...\n");
+			return -1;
+		}
+	}
+
+	ptr = map_sysmem(store_addr, len);
+	memcpy(ptr, src, len);
+	unmap_sysmem(ptr);
+
+	ctx->daddr += len;
+	ctx->size += len;
+	ctx->block_count++;
+	if (ctx->block_count % 10 == 0) {
+		putc('#');
+		if (ctx->block_count % (65 * 10) == 0)
+			puts("\n\t ");
+	}
+
+	return 0;
+}
+
 static void *tftp_open(const char *fname, const char *mode, u8_t is_write)
 {
 	return NULL;
@@ -71,17 +113,9 @@
 	struct tftp_ctx *ctx = handle;
 	struct pbuf *q;
 
-	for (q = p; q; q = q->next) {
-		memcpy((void *)ctx->daddr, q->payload, q->len);
-		ctx->daddr += q->len;
-		ctx->size += q->len;
-		ctx->block_count++;
-		if (ctx->block_count % 10 == 0) {
-			putc('#');
-			if (ctx->block_count % (65 * 10) == 0)
-				puts("\n\t ");
-		}
-	}
+	for (q = p; q; q = q->next)
+		if (store_block(ctx, q->payload, q->len) < 0)
+			return -1;
 
 	return 0;
 }