net: Define usercopy region in struct proto slab cache

In support of usercopy hardening, this patch defines a region in the
struct proto slab cache in which userspace copy operations are allowed.
Some protocols need to copy objects to/from userspace, and they can
declare the region via their proto structure with the new usersize and
useroffset fields. Initially, if no region is specified (usersize ==
0), the entire field is marked as whitelisted. This allows protocols
to be whitelisted in subsequent patches. Once all protocols have been
annotated, the full-whitelist default can be removed.

This region is known as the slab cache's usercopy region. Slab caches
can now check that each dynamically sized 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 <dave@nullcore.net>
[kees: adjust commit log, split off per-proto patches]
[kees: add logic for by-default full-whitelist]
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index 79e1a2c7912c..b77a710ee831 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1112,6 +1112,8 @@ struct proto {
 	struct kmem_cache	*slab;
 	unsigned int		obj_size;
 	slab_flags_t		slab_flags;
+	size_t			useroffset;	/* Usercopy region offset */
+	size_t			usersize;	/* Usercopy region size */
 
 	struct percpu_counter	*orphan_count;