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Message-ID: <58fd7e35-ba6c-432e-8e02-9c5476c854b4@kili.mountain>
Date: Wed, 31 May 2023 10:48:09 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: NeilBrown <neilb@...e.de>
Cc: Stanislav Kinsbursky <skinsbursky@...allels.com>,
Chuck Lever <chuck.lever@...cle.com>,
Jeff Layton <jlayton@...nel.org>,
Trond Myklebust <trond.myklebust@...merspace.com>,
Anna Schumaker <anna@...nel.org>,
"J. Bruce Fields" <bfields@...hat.com>, linux-nfs@...r.kernel.org,
netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] nfsd: fix double fget() bug in __write_ports_addfd()
On Wed, May 31, 2023 at 08:27:43AM +1000, NeilBrown wrote:
> On Mon, 29 May 2023, Dan Carpenter wrote:
> > The bug here is that you cannot rely on getting the same socket
> > from multiple calls to fget() because userspace can influence
> > that. This is a kind of double fetch bug.
> >
> > The fix is to delete the svc_alien_sock() function and insted do
> > the checking inside the svc_addsock() function.
>
> Hi,
> I definitely agree with the change to pass the 'net' into
> svc_addsock(), and check the the fd has the correct net.
>
> I'm not sure I agree with the removal of the svc_alien_sock() test. It
> is best to perform sanity tests before allocation things, and
> nfsd_create_serv() can create a new 'serv' - though most often it just
> incs the refcount.
That's true. But the other philosophical rule is that we shouldn't
optimize for the failure path. If someone gives us bad data they
deserve a slow down.
I also think leaving svc_alien_sock() is a trap for the unwary because
it will lead to more double fget() bugs. The svc_alien_sock() function
is weird because it returns false on success and false on failure and
true for alien sock.
>
> Maybe instead svc_alien_sock() could return the struct socket (if
> successful), and it could be passed to svc_addsock()???
>
> I would probably then change the name of svc_alien_sock()
Yeah, because we don't want alien sockets, we want Earth sockets.
Doing this is much more complicated... The name svc_get_earth_sock()
is just a joke. Tell me what name to use if we decide to go this
route.
To be honest, I would probably still go with my v1 patch.
regards,
dan carpenter
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index e0e98b40a6e5d..affcd44f03d6b 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -689,6 +689,7 @@ static ssize_t __write_ports_names(char *buf, struct net *net)
*/
static ssize_t __write_ports_addfd(char *buf, struct net *net, const struct cred *cred)
{
+ struct socket *so;
char *mesg = buf;
int fd, err;
struct nfsd_net *nn = net_generic(net, nfsd_net_id);
@@ -698,22 +699,30 @@ static ssize_t __write_ports_addfd(char *buf, struct net *net, const struct cred
return -EINVAL;
trace_nfsd_ctl_ports_addfd(net, fd);
- if (svc_alien_sock(net, fd)) {
+ so = svc_get_earth_sock(net, fd);
+ if (!so) {
printk(KERN_ERR "%s: socket net is different to NFSd's one\n", __func__);
return -EINVAL;
}
err = nfsd_create_serv(net);
if (err != 0)
- return err;
+ goto out_put_sock;
- err = svc_addsock(nn->nfsd_serv, fd, buf, SIMPLE_TRANSACTION_LIMIT, cred);
+ err = svc_addsock(nn->nfsd_serv, so, buf, SIMPLE_TRANSACTION_LIMIT, cred);
+ if (err)
+ goto out_put_net;
- if (err >= 0 &&
- !nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
+ if (!nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
svc_get(nn->nfsd_serv);
nfsd_put(net);
+ return 0;
+
+out_put_net:
+ nfsd_put(net);
+out_put_sock:
+ sockfd_put(so);
return err;
}
diff --git a/include/linux/sunrpc/svcsock.h b/include/linux/sunrpc/svcsock.h
index d16ae621782c0..2422d260591bb 100644
--- a/include/linux/sunrpc/svcsock.h
+++ b/include/linux/sunrpc/svcsock.h
@@ -61,8 +61,8 @@ int svc_recv(struct svc_rqst *, long);
void svc_send(struct svc_rqst *rqstp);
void svc_drop(struct svc_rqst *);
void svc_sock_update_bufs(struct svc_serv *serv);
-bool svc_alien_sock(struct net *net, int fd);
-int svc_addsock(struct svc_serv *serv, const int fd,
+struct socket *svc_get_earth_sock(struct net *net, int fd);
+int svc_addsock(struct svc_serv *serv, struct socket *so,
char *name_return, const size_t len,
const struct cred *cred);
void svc_init_xprt_sock(void);
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 46845cb6465d7..78f6ae9fa42d4 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -1474,21 +1474,20 @@ static struct svc_sock *svc_setup_socket(struct svc_serv *serv,
return svsk;
}
-bool svc_alien_sock(struct net *net, int fd)
+struct socket *svc_get_earth_sock(struct net *net, int fd)
{
int err;
struct socket *sock = sockfd_lookup(fd, &err);
- bool ret = false;
if (!sock)
- goto out;
- if (sock_net(sock->sk) != net)
- ret = true;
- sockfd_put(sock);
-out:
- return ret;
+ return NULL;
+ if (sock_net(sock->sk) != net) {
+ sockfd_put(sock);
+ return NULL;
+ }
+ return sock;
}
-EXPORT_SYMBOL_GPL(svc_alien_sock);
+EXPORT_SYMBOL_GPL(svc_get_earth_sock);
/**
* svc_addsock - add a listener socket to an RPC service
@@ -1502,36 +1501,27 @@ EXPORT_SYMBOL_GPL(svc_alien_sock);
* Name is terminated with '\n'. On error, returns a negative errno
* value.
*/
-int svc_addsock(struct svc_serv *serv, const int fd, char *name_return,
+int svc_addsock(struct svc_serv *serv, struct socket *so, char *name_return,
const size_t len, const struct cred *cred)
{
- int err = 0;
- struct socket *so = sockfd_lookup(fd, &err);
struct svc_sock *svsk = NULL;
struct sockaddr_storage addr;
struct sockaddr *sin = (struct sockaddr *)&addr;
int salen;
- if (!so)
- return err;
- err = -EAFNOSUPPORT;
if ((so->sk->sk_family != PF_INET) && (so->sk->sk_family != PF_INET6))
- goto out;
- err = -EPROTONOSUPPORT;
+ return -EAFNOSUPPORT;
if (so->sk->sk_protocol != IPPROTO_TCP &&
so->sk->sk_protocol != IPPROTO_UDP)
- goto out;
- err = -EISCONN;
+ return -EPROTONOSUPPORT;
if (so->state > SS_UNCONNECTED)
- goto out;
- err = -ENOENT;
+ return -EISCONN;
if (!try_module_get(THIS_MODULE))
- goto out;
+ return -ENOENT;
svsk = svc_setup_socket(serv, so, SVC_SOCK_DEFAULTS);
if (IS_ERR(svsk)) {
module_put(THIS_MODULE);
- err = PTR_ERR(svsk);
- goto out;
+ return PTR_ERR(svsk);
}
salen = kernel_getsockname(svsk->sk_sock, sin);
if (salen >= 0)
@@ -1539,9 +1529,6 @@ int svc_addsock(struct svc_serv *serv, const int fd, char *name_return,
svsk->sk_xprt.xpt_cred = get_cred(cred);
svc_add_new_perm_xprt(serv, &svsk->sk_xprt);
return svc_one_sock_name(svsk, name_return, len);
-out:
- sockfd_put(so);
- return err;
}
EXPORT_SYMBOL_GPL(svc_addsock);
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