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udp: preserve head state for IP_CMSG_PASSSEC 

Paul Moore reported a SELinux/IP_PASSSEC regression
caused by missing skb->sp at recvmsg() time. We need to
preserve the skb head state to process the IP_CMSG_PASSSEC
cmsg.

With this commit we avoid releasing the skb head state in the
BH even if a secpath is attached to the current skb, and stores
the skb status (with/without head states) in the scratch area,
so that we can access it at skb deallocation time, without
incurring in cache-miss penalties.

This also avoids misusing the skb CB for ipv6 packets,
as introduced by the commit 0ddf3fb2c4 ("udp: preserve
skb->dst if required for IP options processing").

Clean a bit the scratch area helpers implementation, to
reduce the code differences between 32 and 64 bits build.

Reported-by: Paul Moore <paul@paul-moore.com>
Fixes: 0a463c78d2 ("udp: avoid a cache miss on dequeue")
Fixes: 0ddf3fb2c4 ("udp: preserve skb->dst if required for IP options processing")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Tested-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni 2017-07-25 17:57:47 +02:00 committed by David S. Miller
parent 9f9e772da2
commit dce4551cb2
2 changed files with 47 additions and 38 deletions
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33
include/net/udp.h
View File

@ -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 are embedded 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

52
net/ipv4/udp.c
View File

@ -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);
}
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;
}
static int udp_skb_truesize(struct sk_buff *skb)
{
return skb->dev_scratch;
}
#endif
if (likely(!skb->_skb_refdst))
scratch->_tsize_state |= UDP_SKB_IS_STATELESS;
}
static int udp_skb_truesize(struct sk_buff *skb)
{
return udp_skb_scratch(skb)->_tsize_state & ~UDP_SKB_IS_STATELESS;
}
static bool udp_skb_has_head_state(struct sk_buff *skb)
{
return !(udp_skb_scratch(skb)->_tsize_state & UDP_SKB_IS_STATELESS);
}
/* 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);