[PPP]: add PPP MPPE encryption module

From: Matt Domsch <Matt_Domsch@dell.com>

The patch below implements the Microsoft Point-to-Point Encryption method
as a PPP compressor/decompressor.  This is necessary for Linux clients and
servers to interoperate with Microsoft Point-to-Point Tunneling Protocol
(PPTP) servers (either Microsoft PPTP servers or the poptop project) which
use MPPE to encrypt data when creating a VPN.

This patch differs from the kernel_ppp_mppe DKMS pacakge at
pptpclient.sourceforge.net by utilizing the kernel crypto routines rather
than providing its own SHA1 and arcfour implementations.

Minor changes to ppp_generic.c try to prevent a link from disabling
compression (in our case, the encryption) after it has started using
compression (encryption).

Feedback to <pptpclient-devel@lists.sourceforge.net> please.

Signed-off-by: Matt Domsch <Matt_Domsch@dell.com>
Cc: James Cameron <james.cameron@hp.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Brice Goglin <Brice.Goglin@ens-lyon.org>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 86 insertions, 0 deletions

diff --git a/drivers/net/ppp_mppe.h b/drivers/net/ppp_mppe.h
new file mode 100644
index 00000000000..7a14e058c66
--- /dev/null
+++ b/drivers/net/ppp_mppe.h
@@ -0,0 +1,86 @@
+#define MPPE_PAD                4      /* MPPE growth per frame */
+#define MPPE_MAX_KEY_LEN       16      /* largest key length (128-bit) */
+
+/* option bits for ccp_options.mppe */
+#define MPPE_OPT_40            0x01    /* 40 bit */
+#define MPPE_OPT_128           0x02    /* 128 bit */
+#define MPPE_OPT_STATEFUL      0x04    /* stateful mode */
+/* unsupported opts */
+#define MPPE_OPT_56            0x08    /* 56 bit */
+#define MPPE_OPT_MPPC          0x10    /* MPPC compression */
+#define MPPE_OPT_D             0x20    /* Unknown */
+#define MPPE_OPT_UNSUPPORTED (MPPE_OPT_56|MPPE_OPT_MPPC|MPPE_OPT_D)
+#define MPPE_OPT_UNKNOWN       0x40    /* Bits !defined in RFC 3078 were set */
+
+/*
+ * This is not nice ... the alternative is a bitfield struct though.
+ * And unfortunately, we cannot share the same bits for the option
+ * names above since C and H are the same bit.  We could do a u_int32
+ * but then we have to do a htonl() all the time and/or we still need
+ * to know which octet is which.
+ */
+#define MPPE_C_BIT             0x01    /* MPPC */
+#define MPPE_D_BIT             0x10    /* Obsolete, usage unknown */
+#define MPPE_L_BIT             0x20    /* 40-bit */
+#define MPPE_S_BIT             0x40    /* 128-bit */
+#define MPPE_M_BIT             0x80    /* 56-bit, not supported */
+#define MPPE_H_BIT             0x01    /* Stateless (in a different byte) */
+
+/* Does not include H bit; used for least significant octet only. */
+#define MPPE_ALL_BITS (MPPE_D_BIT|MPPE_L_BIT|MPPE_S_BIT|MPPE_M_BIT|MPPE_H_BIT)
+
+/* Build a CI from mppe opts (see RFC 3078) */
+#define MPPE_OPTS_TO_CI(opts, ci)              \
+    do {                                       \
+       u_char *ptr = ci; /* u_char[4] */       \
+                                               \
+       /* H bit */                             \
+       if (opts & MPPE_OPT_STATEFUL)           \
+           *ptr++ = 0x0;                       \
+       else                                    \
+           *ptr++ = MPPE_H_BIT;                \
+       *ptr++ = 0;                             \
+       *ptr++ = 0;                             \
+                                               \
+       /* S,L bits */                          \
+       *ptr = 0;                               \
+       if (opts & MPPE_OPT_128)                \
+           *ptr |= MPPE_S_BIT;                 \
+       if (opts & MPPE_OPT_40)                 \
+           *ptr |= MPPE_L_BIT;                 \
+       /* M,D,C bits not supported */          \
+    } while (/* CONSTCOND */ 0)
+
+/* The reverse of the above */
+#define MPPE_CI_TO_OPTS(ci, opts)              \
+    do {                                       \
+       u_char *ptr = ci; /* u_char[4] */       \
+                                               \
+       opts = 0;                               \
+                                               \
+       /* H bit */                             \
+       if (!(ptr[0] & MPPE_H_BIT))             \
+           opts |= MPPE_OPT_STATEFUL;          \
+                                               \
+       /* S,L bits */                          \
+       if (ptr[3] & MPPE_S_BIT)                \
+           opts |= MPPE_OPT_128;               \
+       if (ptr[3] & MPPE_L_BIT)                \
+           opts |= MPPE_OPT_40;                \
+                                               \
+       /* M,D,C bits */                        \
+       if (ptr[3] & MPPE_M_BIT)                \
+           opts |= MPPE_OPT_56;                \
+       if (ptr[3] & MPPE_D_BIT)                \
+           opts |= MPPE_OPT_D;                 \
+       if (ptr[3] & MPPE_C_BIT)                \
+           opts |= MPPE_OPT_MPPC;              \
+                                               \
+       /* Other bits */                        \
+       if (ptr[0] & ~MPPE_H_BIT)               \
+           opts |= MPPE_OPT_UNKNOWN;           \
+       if (ptr[1] || ptr[2])                   \
+           opts |= MPPE_OPT_UNKNOWN;           \
+       if (ptr[3] & ~MPPE_ALL_BITS)            \
+           opts |= MPPE_OPT_UNKNOWN;           \
+    } while (/* CONSTCOND */ 0)