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net: sock_copy() fixes 

Commit e912b1142b
(net: sk_prot_alloc() should not blindly overwrite memory)
took care of not zeroing whole new socket at allocation time.

sock_copy() is another spot where we should be very careful.
We should not set refcnt to a non null value, until
we are sure other fields are correctly setup, or
a lockless reader could catch this socket by mistake,
while not fully (re)initialized.

This patch puts sk_node & sk_refcnt to the very beginning
of struct sock to ease sock_copy() & sk_prot_alloc() job.

We add appropriate smp_wmb() before sk_refcnt initializations
to match our RCU requirements (changes to sock keys should
be committed to memory before sk_refcnt setting)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2009-07-15 23:13:10 +00:00 committed by David S. Miller
parent 303d67c288
commit 4dc6dc7162
2 changed files with 37 additions and 15 deletions
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32
include/net/sock.h
View File

@ -104,15 +104,15 @@ struct net;
/**
* struct sock_common - minimal network layer representation of sockets
* @skc_node: main hash linkage for various protocol lookup tables
* @skc_nulls_node: main hash linkage for UDP/UDP-Lite protocol
* @skc_refcnt: reference count
* @skc_hash: hash value used with various protocol lookup tables
* @skc_family: network address family
* @skc_state: Connection state
* @skc_reuse: %SO_REUSEADDR setting
* @skc_bound_dev_if: bound device index if != 0
* @skc_node: main hash linkage for various protocol lookup tables
* @skc_nulls_node: main hash linkage for UDP/UDP-Lite protocol
* @skc_bind_node: bind hash linkage for various protocol lookup tables
* @skc_refcnt: reference count
* @skc_hash: hash value used with various protocol lookup tables
* @skc_prot: protocol handlers inside a network family
* @skc_net: reference to the network namespace of this socket
*
@ -120,17 +120,21 @@ struct net;
* for struct sock and struct inet_timewait_sock.
*/
struct sock_common {
unsigned short skc_family;
volatile unsigned char skc_state;
unsigned char skc_reuse;
int skc_bound_dev_if;
/*
* first fields are not copied in sock_copy()
*/
union {
struct hlist_node skc_node;
struct hlist_nulls_node skc_nulls_node;
};
struct hlist_node skc_bind_node;
atomic_t skc_refcnt;
unsigned int skc_hash;
unsigned short skc_family;
volatile unsigned char skc_state;
unsigned char skc_reuse;
int skc_bound_dev_if;
struct hlist_node skc_bind_node;
struct proto *skc_prot;
#ifdef CONFIG_NET_NS
struct net *skc_net;
@ -208,15 +212,17 @@ struct sock {
* don't add nothing before this first member (__sk_common) --acme
*/
struct sock_common __sk_common;
#define sk_node __sk_common.skc_node
#define sk_nulls_node __sk_common.skc_nulls_node
#define sk_refcnt __sk_common.skc_refcnt
#define sk_copy_start __sk_common.skc_hash
#define sk_hash __sk_common.skc_hash
#define sk_family __sk_common.skc_family
#define sk_state __sk_common.skc_state
#define sk_reuse __sk_common.skc_reuse
#define sk_bound_dev_if __sk_common.skc_bound_dev_if
#define sk_node __sk_common.skc_node
#define sk_nulls_node __sk_common.skc_nulls_node
#define sk_bind_node __sk_common.skc_bind_node
#define sk_refcnt __sk_common.skc_refcnt
#define sk_hash __sk_common.skc_hash
#define sk_prot __sk_common.skc_prot
#define sk_net __sk_common.skc_net
kmemcheck_bitfield_begin(flags);

20
net/core/sock.c
View File

@ -919,13 +919,19 @@ static inline void sock_lock_init(struct sock *sk)
af_family_keys + sk->sk_family);
}
/*
* Copy all fields from osk to nsk but nsk->sk_refcnt must not change yet,
* even temporarly, because of RCU lookups. sk_node should also be left as is.
*/
static void sock_copy(struct sock *nsk, const struct sock *osk)
{
#ifdef CONFIG_SECURITY_NETWORK
void *sptr = nsk->sk_security;
#endif
memcpy(nsk, osk, osk->sk_prot->obj_size);
BUILD_BUG_ON(offsetof(struct sock, sk_copy_start) !=
sizeof(osk->sk_node) + sizeof(osk->sk_refcnt));
memcpy(&nsk->sk_copy_start, &osk->sk_copy_start,
osk->sk_prot->obj_size - offsetof(struct sock, sk_copy_start));
#ifdef CONFIG_SECURITY_NETWORK
nsk->sk_security = sptr;
security_sk_clone(osk, nsk);
@ -1140,6 +1146,11 @@ struct sock *sk_clone(const struct sock *sk, const gfp_t priority)
newsk->sk_err = 0;
newsk->sk_priority = 0;
/*
* Before updating sk_refcnt, we must commit prior changes to memory
* (Documentation/RCU/rculist_nulls.txt for details)
*/
smp_wmb();
atomic_set(&newsk->sk_refcnt, 2);
/*
@ -1855,6 +1866,11 @@ void sock_init_data(struct socket *sock, struct sock *sk)
sk->sk_stamp = ktime_set(-1L, 0);
/*
* Before updating sk_refcnt, we must commit prior changes to memory
* (Documentation/RCU/rculist_nulls.txt for details)
*/
smp_wmb();
atomic_set(&sk->sk_refcnt, 1);
atomic_set(&sk->sk_wmem_alloc, 1);
atomic_set(&sk->sk_drops, 0);