sk-filter: Add ability to get socket filter program (v2)

The SO_ATTACH_FILTER option is set only. I propose to add the get
ability by using SO_ATTACH_FILTER in getsockopt. To be less
irritating to eyes the SO_GET_FILTER alias to it is declared. This
ability is required by checkpoint-restore project to be able to
save full state of a socket.

There are two issues with getting filter back.

First, kernel modifies the sock_filter->code on filter load, thus in
order to return the filter element back to user we have to decode it
into user-visible constants. Fortunately the modification in question
is interconvertible.

Second, the BPF_S_ALU_DIV_K code modifies the command argument k to
speed up the run-time division by doing kernel_k = reciprocal(user_k).
Bad news is that different user_k may result in same kernel_k, so we
can't get the original user_k back. Good news is that we don't have
to do it. What we need to is calculate a user2_k so, that

  reciprocal(user2_k) == reciprocal(user_k) == kernel_k

i.e. if it's re-loaded back the compiled again value will be exactly
the same as it was. That said, the user2_k can be calculated like this

  user2_k = reciprocal(kernel_k)

with an exception, that if kernel_k == 0, then user2_k == 1.

The optlen argument is treated like this -- when zero, kernel returns
the amount of sock_fprog elements in filter, otherwise it should be
large enough for the sock_fprog array.

changes since v1:
* Declared SO_GET_FILTER in all arch headers
* Added decode of vlan-tag codes

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

19 files changed, 153 insertions, 0 deletions

diff --git a/arch/alpha/include/asm/socket.h b/arch/alpha/include/asm/socket.h
index 7d2f75be932e..0087d053b77f 100644
--- a/arch/alpha/include/asm/socket.h
+++ b/arch/alpha/include/asm/socket.h
@@ -47,6 +47,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/avr32/include/uapi/asm/socket.h b/arch/avr32/include/uapi/asm/socket.h
index a473f8c6a9aa..486df68abeec 100644
--- a/arch/avr32/include/uapi/asm/socket.h
+++ b/arch/avr32/include/uapi/asm/socket.h
@@ -40,6 +40,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/cris/include/asm/socket.h b/arch/cris/include/asm/socket.h
index ae52825021af..b681b043f6c8 100644
--- a/arch/cris/include/asm/socket.h
+++ b/arch/cris/include/asm/socket.h
@@ -42,6 +42,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP           29
diff --git a/arch/frv/include/uapi/asm/socket.h b/arch/frv/include/uapi/asm/socket.h
index a5b1d7dbb205..871f89b7fbda 100644
--- a/arch/frv/include/uapi/asm/socket.h
+++ b/arch/frv/include/uapi/asm/socket.h
@@ -40,6 +40,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/h8300/include/asm/socket.h b/arch/h8300/include/asm/socket.h
index ec4554e7b04b..90a2e573c7e6 100644
--- a/arch/h8300/include/asm/socket.h
+++ b/arch/h8300/include/asm/socket.h
@@ -40,6 +40,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/ia64/include/uapi/asm/socket.h b/arch/ia64/include/uapi/asm/socket.h
index 41fc28a4a18a..23d6759bb57b 100644
--- a/arch/ia64/include/uapi/asm/socket.h
+++ b/arch/ia64/include/uapi/asm/socket.h
@@ -49,6 +49,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/m32r/include/asm/socket.h b/arch/m32r/include/asm/socket.h
index a15f40b52783..5e7088a26726 100644
--- a/arch/m32r/include/asm/socket.h
+++ b/arch/m32r/include/asm/socket.h
@@ -40,6 +40,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/m68k/include/asm/socket.h b/arch/m68k/include/asm/socket.h
index d1be684edf97..285da3b6ad92 100644
--- a/arch/m68k/include/asm/socket.h
+++ b/arch/m68k/include/asm/socket.h
@@ -40,6 +40,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index c5ed59549cb8..17307ab90474 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -63,6 +63,7 @@ To add: #define SO_REUSEPORT 0x0200	/* Allow local address and port reuse.  */
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/mn10300/include/uapi/asm/socket.h b/arch/mn10300/include/uapi/asm/socket.h
index 820463a484b8..af5366bbfe62 100644
--- a/arch/mn10300/include/uapi/asm/socket.h
+++ b/arch/mn10300/include/uapi/asm/socket.h
@@ -40,6 +40,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/parisc/include/asm/socket.h b/arch/parisc/include/asm/socket.h
index 1b52c2c31a7a..d9ff4731253b 100644
--- a/arch/parisc/include/asm/socket.h
+++ b/arch/parisc/include/asm/socket.h
@@ -48,6 +48,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        0x401a
 #define SO_DETACH_FILTER        0x401b
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_ACCEPTCONN           0x401c
 
diff --git a/arch/powerpc/include/uapi/asm/socket.h b/arch/powerpc/include/uapi/asm/socket.h
index 3d5179bb122f..eb0b1864d400 100644
--- a/arch/powerpc/include/uapi/asm/socket.h
+++ b/arch/powerpc/include/uapi/asm/socket.h
@@ -47,6 +47,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26
 #define SO_DETACH_FILTER        27
+#define SO_GET_FILTER           SO_ATTACH_FILTER
 
 #define SO_PEERNAME             28
 #define SO_TIMESTAMP            29
diff --git a/arch/s390/include/uapi/asm/socket.h b/arch/s390/include/uapi/asm/socket.h
index 69718cd6d635..436d07c23be8 100644
--- a/arch/s390/include/uapi/asm/socket.h
+++ b/arch/s390/include/uapi/asm/socket.h
@@ -46,6 +46,7 @@
 /* Socket filtering */
 #define SO_ATTACH_FILTER        26