pxe: Ensure we don't overflow bootargs

On a couple of platforms I've tripped over long PXE append lines overflowing
this array, due to having CONFIG_SYS_CBSIZE == 256. When doing preseeded Debian
installs it's pretty trivial to exceed that.

Since the symptom can be a silent hang or a crash add a check. Of course the
affected boards would also need an increased CBSIZE to actually work.

Note that due to the printing of the final bootargs string CONFIG_SYS_PBSIZE
also needs to be sufficiently large.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
[trini: Use %zd not %d in printf for all args]
Signed-off-by: Tom Rini <trini@ti.com>

common/cmd_pxe.c

@@ -674,6 +674,15 @@ static int label_boot(cmd_tbl_t *cmdtp, struct pxe_label *label)
 		char bootargs[CONFIG_SYS_CBSIZE] = "";
 		char finalbootargs[CONFIG_SYS_CBSIZE];
 
+		if (strlen(label->append ?: "") +
+		    strlen(ip_str) + strlen(mac_str) + 1 > sizeof(bootargs)) {
+			printf("bootarg overflow %zd+%zd+%zd+1 > %zd\n",
+			       strlen(label->append ?: ""),
+			       strlen(ip_str), strlen(mac_str),
+			       sizeof(bootargs));
+			return 1;
+		}
+
 		if (label->append)
 			strcpy(bootargs, label->append);
 		strcat(bootargs, ip_str);