[PPP]: Fix osize too small errors when decoding mppe.

The mppe_decompress() function required a buffer that is 1 byte too
small when receiving a message of mru size. This fixes buffer
allocation to prevent this from occurring.

Signed-off-by: Konstantin Sharlaimov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ppp_generic.c

···
 		goto err;
 
 	if (proto == PPP_COMP) {
-		ns = dev_alloc_skb(ppp->mru + PPP_HDRLEN);
+		int obuff_size;
+
+		switch(ppp->rcomp->compress_proto) {
+		case CI_MPPE:
+			obuff_size = ppp->mru + PPP_HDRLEN + 1;
+			break;
+		default:
+			obuff_size = ppp->mru + PPP_HDRLEN;
+			break;
+		}
+
+		ns = dev_alloc_skb(obuff_size);
 		if (ns == 0) {
 			printk(KERN_ERR "ppp_decompress_frame: no memory\n");
 			goto err;