kbuild: replace unbounded sprintf call in modpost

The modpost tool could overflow its stack buffer if someone was running
with an insane shell environment. Regardless, it's technically a bug,
so this fixes it to truncate the string instead of seg-faulting.

Found by Coverity.
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/mod/sumversion.c

@@ -416,7 +416,7 @@ void get_src_version(const char *modname, char sum[], unsigned sumlen)
 		basename = strrchr(modname, '/') + 1;
 	else
 		basename = modname;
-	sprintf(filelist, "%s/%.*s.mod", modverdir,
+	snprintf(filelist, sizeof(filelist), "%s/%.*s.mod", modverdir,
 		(int) strlen(basename) - 2, basename);
 
 	file = grab_file(filelist, &len);