[patch 21/21] knfsd: Fix a race in closing NFSd connections.

Greg KH
2007-02-21T01:41:03Z

[-- Attachment #1: knfsd-fix-a-race-in-closing-nfsd-connections.patch --]
[-- Type: text/plain, Size: 6523 bytes --]

-stable review patch. If anyone has any objections, please let us know.

------------------
If you lose this race, it can iput a socket inode twice and you
get a BUG in fs/inode.c

When I added the option for user-space to close a socket,
I added some cruft to svc_delete_socket so that I could call
that function when closing a socket per user-space request.

This was the wrong thing to do. I should have just set SK_CLOSE
and let normal mechanisms do the work.

Not only wrong, but buggy. The locking is all wrong and it openned
up a race where-by a socket could be closed twice.

So this patch:
Introduces svc_close_socket which sets SK_CLOSE then either leave
the close up to a thread, or calls svc_delete_socket if it can
get SK_BUSY.

Adds a bias to sk_busy which is removed when SK_DEAD is set,
This avoid races around shutting down the socket.

Changes several 'spin_lock' to 'spin_lock_bh' where the _bh
was missing.

Bugzilla-url: http://bugzilla.kernel.org/show_bug.cgi?id=7916

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
include/linux/sunrpc/svcsock.h | 2 -
net/sunrpc/svc.c | 4 +--
net/sunrpc/svcsock.c | 52 +++++++++++++++++++++++++++++------------
3 files changed, 41 insertions(+), 17 deletions(-)

--- linux-2.6.19.4.orig/include/linux/sunrpc/svcsock.h
+++ linux-2.6.19.4/include/linux/sunrpc/svcsock.h
@@ -63,7 +63,7 @@ struct svc_sock {
* Function prototypes.
*/
int svc_makesock(struct svc_serv *, int, unsigned short);
-void svc_delete_socket(struct svc_sock *);
+void svc_close_socket(struct svc_sock *);
int svc_recv(struct svc_rqst *, long);
int svc_send(struct svc_rqst *);
void svc_drop(struct svc_rqst *);
--- linux-2.6.19.4.orig/net/sunrpc/svc.c
+++ linux-2.6.19.4/net/sunrpc/svc.c
@@ -387,7 +387,7 @@ svc_destroy(struct svc_serv *serv)
svsk = list_entry(serv->sv_tempsocks.next,
struct svc_sock,
sk_list);
- svc_delete_socket(svsk);
+ svc_close_socket(svsk);
}
if (serv->sv_shutdown)
serv->sv_shutdown(serv);
@@ -396,7 +396,7 @@ svc_destroy(struct svc_serv *serv)
svsk = list_entry(serv->sv_permsocks.next,
struct svc_sock,
sk_list);
- svc_delete_socket(svsk);
+ svc_close_socket(svsk);
}

cache_clean_deferred(serv);
--- linux-2.6.19.4.orig/net/sunrpc/svcsock.c
+++ linux-2.6.19.4/net/sunrpc/svcsock.c
@@ -61,6 +61,12 @@
* after a clear, the socket must be read/accepted
* if this succeeds, it must be set again.
* SK_CLOSE can set at any time. It is never cleared.
+ * sk_inuse contains a bias of '1' until SK_DEAD is set.
+ * so when sk_inuse hits zero, we know the socket is dead
+ * and no-one is using it.
+ * SK_DEAD can only be set while SK_BUSY is held which ensures
+ * no other thread will be using the socket or will try to
+ * set SK_DEAD.
*
*/

@@ -69,6 +75,7 @@

static struct svc_sock *svc_setup_socket(struct svc_serv *, struct socket *,
int *errp, int pmap_reg);
+static void svc_delete_socket(struct svc_sock *svsk);
static void svc_udp_data_ready(struct sock *, int);
static int svc_udp_recvfrom(struct svc_rqst *);
static int svc_udp_sendto(struct svc_rqst *);
@@ -299,8 +306,9 @@ void svc_reserve(struct svc_rqst *rqstp,
static inline void
svc_sock_put(struct svc_sock *svsk)
{
- if (atomic_dec_and_test(&svsk->sk_inuse) &&
- test_bit(SK_DEAD, &svsk->sk_flags)) {
+ if (atomic_dec_and_test(&svsk->sk_inuse)) {
+ BUG_ON(! test_bit(SK_DEAD, &svsk->sk_flags));
+
dprintk("svc: releasing dead socket\n");
if (svsk->sk_sock->file)
sockfd_put(svsk->sk_sock);
@@ -490,7 +498,7 @@ svc_sock_names(char *buf, struct svc_ser

if (!serv)
return 0;
- spin_lock(&serv->sv_lock);
+ spin_lock_bh(&serv->sv_lock);
list_for_each_entry(svsk, &serv->sv_permsocks, sk_list) {
int onelen = one_sock_name(buf+len, svsk);
if (toclose && strcmp(toclose, buf+len) == 0)
@@ -498,12 +506,12 @@ svc_sock_names(char *buf, struct svc_ser
else
len += onelen;
}
- spin_unlock(&serv->sv_lock);
+ spin_unlock_bh(&serv->sv_lock);
if (closesk)
/* Should unregister with portmap, but you cannot
* unregister just one protocol...
*/
- svc_delete_socket(closesk);
+ svc_close_socket(closesk);
else if (toclose)
return -ENOENT;
return len;
@@ -653,6 +661,11 @@ svc_udp_recvfrom(struct svc_rqst *rqstp)
return svc_deferred_recv(rqstp);
}

+ if (test_bit(SK_CLOSE, &svsk->sk_flags)) {
+ svc_delete_socket(svsk);
+ return 0;
+ }
+
clear_bit(SK_DATA, &svsk->sk_flags);
while ((skb = skb_recv_datagram(svsk->sk_sk, 0, 1, &err)) == NULL) {
if (err == -EAGAIN) {
@@ -1142,7 +1155,8 @@ svc_tcp_sendto(struct svc_rqst *rqstp)
rqstp->rq_sock->sk_server->sv_name,
(sent<0)?"got error":"sent only",
sent, xbufp->len);
- svc_delete_socket(rqstp->rq_sock);
+ set_bit(SK_CLOSE, &rqstp->rq_sock->sk_flags);
+ svc_sock_enqueue(rqstp->rq_sock);
sent = -EAGAIN;
}
return sent;
@@ -1461,7 +1475,7 @@ svc_setup_socket(struct svc_serv *serv,
svsk->sk_odata = inet->sk_data_ready;
svsk->sk_owspace = inet->sk_write_space;
svsk->sk_server = serv;
- atomic_set(&svsk->sk_inuse, 0);
+ atomic_set(&svsk->sk_inuse, 1);
svsk->sk_lastrecv = get_seconds();
spin_lock_init(&svsk->sk_defer_lock);
INIT_LIST_HEAD(&svsk->sk_deferred);
@@ -1582,7 +1596,7 @@ bummer:
/*
* Remove a dead socket
*/
-void
+static void
svc_delete_socket(struct svc_sock *svsk)
{
struct svc_serv *serv;
@@ -1608,16 +1622,26 @@ svc_delete_socket(struct svc_sock *svsk)
* while still attached to a queue, the queue itself
* is about to be destroyed (in svc_destroy).
*/
- if (!test_and_set_bit(SK_DEAD, &svsk->sk_flags))
+ if (!test_and_set_bit(SK_DEAD, &svsk->sk_flags)) {
+ BUG_ON(atomic_read(&svsk->sk_inuse)<2);
+ atomic_dec(&svsk->sk_inuse);
if (test_bit(SK_TEMP, &svsk->sk_flags))
serv->sv_tmpcnt--;
+ }

- /* This atomic_inc should be needed - svc_delete_socket
- * should have the semantic of dropping a reference.
- * But it doesn't yet....
- */
- atomic_inc(&svsk->sk_inuse);
spin_unlock_bh(&serv->sv_lock);
+}
+
+void svc_close_socket(struct svc_sock *svsk)
+{
+ set_bit(SK_CLOSE, &svsk->sk_flags);
+ if (test_and_set_bit(SK_BUSY, &svsk->sk_flags))
+ /* someone else will have to effect the close */
+ return;
+
+ atomic_inc(&svsk->sk_inuse);
+ svc_delete_socket(svsk);
+ clear_bit(SK_BUSY, &svsk->sk_flags);
svc_sock_put(svsk);
}

--