[PATCH v3 19/31] ip: Define usercopy region in IP proto slab cache

[Kees Cook]

From: David Windsor <d...@nullcore.net>

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 <d...@nullcore.net>
[kees: split from network patch, provide usage trace]
Cc: "David S. Miller" <da...@davemloft.net>
Cc: Alexey Kuznetsov <kuz...@ms2.inr.ac.ru>
Cc: Hideaki YOSHIFUJI <yoshf...@linux-ipv6.org>
Cc: net...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 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 33b70bfd1122..1b6fa4195ac9 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -970,6 +970,8 @@ 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 e4462b0ff801..041d1cd5e774 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -1268,6 +1268,8 @@ 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