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Date: Mon, 24 Jul 2017 18:09:15 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Paul Moore <paul@...l-moore.com>
Cc: netdev@...r.kernel.org, selinux@...ho.nsa.gov
Subject: Re: SELinux/IP_PASSSEC regression in 4.13-rcX
Hi,
On Mon, 2017-07-24 at 10:42 -0400, Paul Moore wrote:
> The change in behavior for userspace makes me a little nervous as
> there is no way of knowing how any random application may be coded.
> Even if we are confident that the majority of applications set
> IP_PASSSEC before calling bind(), we are likely still stuck with a few
> that will break, and that means a lot of hard to debug problem
> reports.
>
> I would feel much more comfortable if we could preserve the existing behavior.
I agree, we must preserve the original behavior.
Re-thinking about the problem, checking skb->sp in the BH, and storing
the status in the scratch area should both fix the issue in a sane way
and preserve the optimization.
Something like the code below. Could you please try in your
environment? (or point me to simple reproducer ;-)
There are some cosmetics changes vs the previous iteration, but the
only relevant difference is that now the code always preserve skb->sb,
as per the pre-0a463c78d25b kernel behavior.
Thank you!
Paolo
---
diff --git a/include/net/udp.h b/include/net/udp.h
index 972ce4b..8d2c406 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -305,33 +305,44 @@ struct sock *udp6_lib_lookup_skb(struct sk_buff *skb,
/* UDP uses skb->dev_scratch to cache as much information as possible and avoid
* possibly multiple cache miss on dequeue()
*/
-#if BITS_PER_LONG == 64
-
-/* truesize, len and the bit needed to compute skb_csum_unnecessary will be on
- * cold cache lines at recvmsg time.
- * skb->len can be stored on 16 bits since the udp header has been already
- * validated and pulled.
- */
struct udp_dev_scratch {
- u32 truesize;
+ /* skb->truesize and the stateless bit embeded in a single field;
+ * do not use a bitfield since the compiler emits better/smaller code
+ * this way
+ */
+ u32 _tsize_state;
+
+#if BITS_PER_LONG == 64
+ /* len and the bit needed to compute skb_csum_unnecessary
+ * will be on cold cache lines at recvmsg time.
+ * skb->len can be stored on 16 bits since the udp header has been
+ * already validated and pulled.
+ */
u16 len;
bool is_linear;
bool csum_unnecessary;
+#endif
};
+static inline struct udp_dev_scratch* udp_skb_scratch(struct sk_buff *skb)
+{
+ return (struct udp_dev_scratch *)&skb->dev_scratch;
+}
+
+#if BITS_PER_LONG == 64
static inline unsigned int udp_skb_len(struct sk_buff *skb)
{
- return ((struct udp_dev_scratch *)&skb->dev_scratch)->len;
+ return udp_skb_scratch(skb)->len;
}
static inline bool udp_skb_csum_unnecessary(struct sk_buff *skb)
{
- return ((struct udp_dev_scratch *)&skb->dev_scratch)->csum_unnecessary;
+ return udp_skb_scratch(skb)->csum_unnecessary;
}
static inline bool udp_skb_is_linear(struct sk_buff *skb)
{
- return ((struct udp_dev_scratch *)&skb->dev_scratch)->is_linear;
+ return udp_skb_scratch(skb)->is_linear;
}
#else
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index b057653..d243772 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1163,34 +1163,32 @@ int udp_sendpage(struct sock *sk, struct page *page, int offset,
return ret;
}
-#if BITS_PER_LONG == 64
+#define UDP_SKB_IS_STATELESS 0x80000000
+
static void udp_set_dev_scratch(struct sk_buff *skb)
{
- struct udp_dev_scratch *scratch;
+ struct udp_dev_scratch *scratch = udp_skb_scratch(skb);
BUILD_BUG_ON(sizeof(struct udp_dev_scratch) > sizeof(long));
- scratch = (struct udp_dev_scratch *)&skb->dev_scratch;
- scratch->truesize = skb->truesize;
+ scratch->_tsize_state = skb->truesize;
+#if BITS_PER_LONG == 64
scratch->len = skb->len;
scratch->csum_unnecessary = !!skb_csum_unnecessary(skb);
scratch->is_linear = !skb_is_nonlinear(skb);
+#endif
+ if (likely(!skb->_skb_refdst))
+ scratch->_tsize_state |= UDP_SKB_IS_STATELESS;
}
static int udp_skb_truesize(struct sk_buff *skb)
{
- return ((struct udp_dev_scratch *)&skb->dev_scratch)->truesize;
-}
-#else
-static void udp_set_dev_scratch(struct sk_buff *skb)
-{
- skb->dev_scratch = skb->truesize;
+ return udp_skb_scratch(skb)->_tsize_state & ~UDP_SKB_IS_STATELESS;
}
-static int udp_skb_truesize(struct sk_buff *skb)
+static bool udp_skb_has_head_state(struct sk_buff *skb)
{
- return skb->dev_scratch;
+ return !(udp_skb_scratch(skb)->_tsize_state & UDP_SKB_IS_STATELESS);
}
-#endif
/* fully reclaim rmem/fwd memory allocated for skb */
static void udp_rmem_release(struct sock *sk, int size, int partial,
@@ -1388,10 +1386,10 @@ void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len)
unlock_sock_fast(sk, slow);
}
- /* we cleared the head states previously only if the skb lacks any IP
- * options, see __udp_queue_rcv_skb().
+ /* In the more common cases we cleared the head states previously,
+ * see __udp_queue_rcv_skb().
*/
- if (unlikely(IPCB(skb)->opt.optlen > 0))
+ if (unlikely(udp_skb_has_head_state(skb)))
skb_release_head_state(skb);
consume_stateless_skb(skb);
}
@@ -1784,11 +1782,11 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
sk_mark_napi_id_once(sk, skb);
}
- /* At recvmsg() time we need skb->dst to process IP options-related
- * cmsg, elsewhere can we clear all pending head states while they are
- * hot in the cache
+ /* At recvmsg() time we may access skb->dst or skb->sp depending on
+ * the IP options and the cmsg flags, elsewhere can we clear all
+ * pending head states while they are hot in the cache
*/
- if (likely(IPCB(skb)->opt.optlen == 0))
+ if (likely(IPCB(skb)->opt.optlen == 0 && !skb->sp))
skb_release_head_state(skb);
rc = __udp_enqueue_schedule_skb(sk, skb);
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