libata: don't allow sysfs read access to force param

Buffer for force param is deallocated after initialization, so trying
to read it via sysfs results in oops.  Don't allow read access to the
param node.

Spotted by Eric Sesterhenn.
Signed-off-by: NTejun Heo <htejun@gmail.com>
Cc: Eric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/ata/libata-core.c

@@ -106,7 +106,8 @@ static struct ata_force_ent *ata_force_tbl;
 static int ata_force_tbl_size;
 
 static char ata_force_param_buf[PAGE_SIZE] __initdata;
-module_param_string(force, ata_force_param_buf, sizeof(ata_force_param_buf), 0444);
+/* param_buf is thrown away after initialization, disallow read */
+module_param_string(force, ata_force_param_buf, sizeof(ata_force_param_buf), 0);
 MODULE_PARM_DESC(force, "Force ATA configurations including cable type, link speed and transfer mode (see Documentation/kernel-parameters.txt for details)");
 
 int atapi_enabled = 1;