ip: Define usercopy region in IP proto slab cache

From: David Windsor <redacted>

The ICMP filters for IPv4 and IPv6 raw sockets need to be copied to/from
userspace. In support of usercopy hardening, this patch defines a region
in the struct proto slab cache in which userspace copy operations are
allowed.

example usage trace:

    net/ipv4/raw.c:
        raw_seticmpfilter(...):
            ...
            copy_from_user(&raw_sk(sk)->filter, ..., optlen)

        raw_geticmpfilter(...):
            ...
            copy_to_user(..., &raw_sk(sk)->filter, len)

    net/ipv6/raw.c:
        rawv6_seticmpfilter(...):
            ...
            copy_from_user(&raw6_sk(sk)->filter, ..., optlen)

        rawv6_geticmpfilter(...):
            ...
            copy_to_user(..., &raw6_sk(sk)->filter, len)

This region is known as the slab cache's usercopy region. Slab caches can
now check that each copy operation involving cache-managed memory falls
entirely within the slab's usercopy region.

This patch is modified from Brad Spengler/PaX Team's PAX_USERCOPY
whitelisting code in the last public patch of grsecurity/PaX based on my
understanding of the code. Changes or omissions from the original code are
mine and don't reflect the original grsecurity/PaX code.

Signed-off-by: David Windsor <redacted>
[kees: split from network patch, provide usage trace]
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <redacted>
Cc: Hideaki YOSHIFUJI <redacted>
Cc: <redacted>
Signed-off-by: Kees Cook <redacted>
---
 net/ipv4/raw.c | 2 ++
 net/ipv6/raw.c | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index b0bb5d0a30bd..6c7f8d2eb3af 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c

@@ -964,6 +964,8 @@ struct proto raw_prot = {
 	.hash		   = raw_hash_sk,
 	.unhash		   = raw_unhash_sk,
 	.obj_size	   = sizeof(struct raw_sock),
+	.useroffset	   = offsetof(struct raw_sock, filter),
+	.usersize	   = sizeof_field(struct raw_sock, filter),
 	.h.raw_hash	   = &raw_v4_hashinfo,
 #ifdef CONFIG_COMPAT
 	.compat_setsockopt = compat_raw_setsockopt,

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 60be012fe708..27dd9a5f71c6 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c

@@ -1265,6 +1265,8 @@ struct proto rawv6_prot = {
 	.hash		   = raw_hash_sk,
 	.unhash		   = raw_unhash_sk,
 	.obj_size	   = sizeof(struct raw6_sock),
+	.useroffset	   = offsetof(struct raw6_sock, filter),
+	.usersize	   = sizeof_field(struct raw6_sock, filter),
 	.h.raw_hash	   = &raw_v6_hashinfo,
 #ifdef CONFIG_COMPAT
 	.compat_setsockopt = compat_rawv6_setsockopt,

-- 
2.7.4

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