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>

diff --git a/include/net/sock.h b/include/net/sock.h
index 79e1a2c..b77a710 100644 (file)
--- 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;
 

diff --git a/net/core/sock.c b/net/core/sock.c
index c0b5b2f..261e6db 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3151,8 +3151,12 @@ static int req_prot_init(const struct proto *prot)
 int proto_register(struct proto *prot, int alloc_slab)
 {
        if (alloc_slab) {
-               prot->slab = kmem_cache_create(prot->name, prot->obj_size, 0,
+               prot->slab = kmem_cache_create_usercopy(prot->name,
+                                       prot->obj_size, 0,
                                        SLAB_HWCACHE_ALIGN | prot->slab_flags,
+                                       prot->usersize ? prot->useroffset : 0,
+                                       prot->usersize ? prot->usersize
+                                                      : prot->obj_size,
                                        NULL);
 
                if (prot->slab == NULL) {