[PATCH v3 23/31] net: Restrict unwhitelisted proto caches to size 0

[Kees Cook]

Now that protocols have been annotated (the copy of icsk_ca_ops->name
is of an ops field from outside the slab cache):

$ git grep 'copy_.*_user.*sk.*->'
caif/caif_socket.c: copy_from_user(&cf_sk->conn_req.param.data, ov, ol)) {
ipv4/raw.c:   if (copy_from_user(&raw_sk(sk)->filter, optval, optlen))
ipv4/raw.c:       copy_to_user(optval, &raw_sk(sk)->filter, len))
ipv4/tcp.c:       if (copy_to_user(optval, icsk->icsk_ca_ops->name, len))
ipv4/tcp.c:       if (copy_to_user(optval, icsk->icsk_ulp_ops->name, len))
ipv6/raw.c:       if (copy_from_user(&raw6_sk(sk)->filter, optval, optlen))
ipv6/raw.c:           if (copy_to_user(optval, &raw6_sk(sk)->filter, len))
sctp/socket.c: if (copy_from_user(&sctp_sk(sk)->subscribe, optval, optlen))
sctp/socket.c: if (copy_to_user(optval, &sctp_sk(sk)->subscribe, len))
sctp/socket.c: if (copy_to_user(optval, &sctp_sk(sk)->initmsg, len))

we can switch the default proto usercopy region to size 0. Any protocols
needing to add whitelisted regions must annotate the fields with the
useroffset and usersize fields of struct proto.

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.

Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 net/core/sock.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index 832dfb03102e..84cd0b362a02 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3168,9 +3168,7 @@ int proto_register(struct proto *prot, int alloc_slab)
 		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,
+					prot->useroffset, prot->usersize,
 					NULL);
 
 		if (prot->slab == NULL) {
-- 
2.7.4