[PATCH 2.6.21.3] ppp_mppe: account for osize too small errors in mppe_decompress()

[Konstantin Sharlaimov <konstantin.sharlaimov@gmail.com>]

Prevent mppe_decompress() from generating "osize too small" errors when checking
for output buffer size. When receiving a packet of mru size the output buffer
for decrypted data is 1 byte too small since mppe_decompress() tries to account
for possible PFC, however later in code it is assumed no PFC.

Adjusting the check prevented there errors from occurring.

Signed-off-by: Konstantin Sharlaimov <konstantin.sharlaimov@gmail.com>
---
--- linux-2.6.21.3/drivers/net/ppp_mppe.c.orig	2007-06-01 20:57:04.000000000 +1100
+++ linux-2.6.21.3/drivers/net/ppp_mppe.c	2007-06-05 21:46:30.000000000 +1100
@@ -493,14 +493,14 @@ mppe_decompress(void *arg, unsigned char

 	/*
 	 * Make sure we have enough room to decrypt the packet.
-	 * Note that for our test we only subtract 1 byte whereas in
-	 * mppe_compress() we added 2 bytes (+MPPE_OVHD);
-	 * this is to account for possible PFC.
+	 * To account for possible PFC we should only subtract 1
+	 * byte whereas in mppe_compress() we added 2 bytes (+MPPE_OVHD);
+	 * However, we assume no PFC, thus subtracting 2 bytes.
 	 */
-	if (osize < isize - MPPE_OVHD - 1) {
+	if (osize < isize - MPPE_OVHD - 2) {
 		printk(KERN_DEBUG "mppe_decompress[%d]: osize too small! "
 		       "(have: %d need: %d)\n", state->unit,
-		       osize, isize - MPPE_OVHD - 1);
+		       osize, isize - MPPE_OVHD - 2);
 		return DECOMP_ERROR;
 	}
 	osize = isize - MPPE_OVHD - 2;	/* assume no PFC */