Fix memory corruption in console selection

Fix an off-by-two memory error in console selection.

The loop below goes from sel_start to sel_end (inclusive), so it writes
one more character.  This one more character was added to the allocated
size (+1), but it was not multiplied by an UTF-8 multiplier.

This patch fixes a memory corruption when UTF-8 console is used and the
user selects a few characters, all of them 3-byte in UTF-8 (for example
a frame line).

When memory redzones are enabled, a redzone corruption is reported.
When they are not enabled, trashing of random memory occurs.
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/char/selection.c

@@ -268,7 +268,7 @@ int set_selection(const struct tiocl_selection __user *sel, struct tty_struct *t
 
 	/* Allocate a new buffer before freeing the old one ... */
 	multiplier = use_unicode ? 3 : 1;  /* chars can take up to 3 bytes */
-	bp = kmalloc((sel_end-sel_start)/2*multiplier+1, GFP_KERNEL);
+	bp = kmalloc(((sel_end-sel_start)/2+1)*multiplier, GFP_KERNEL);
 	if (!bp) {
 		printk(KERN_WARNING "selection: kmalloc() failed\n");
 		clear_selection();