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SubjectRe: [PATCH/RFC] New module refcounting for net_proto_family
On Thu, 26 Dec 2002, Max Krasnyansky wrote:

Dave,

Did you have a chance to look at the new patch ?

Max

> > Bunch of problems with this patch:
> >
> > 1) Module leak. If try_module_get(npf->owner) works but sock_alloc()
> > fails, we never put the module. It just branches to the "out"
> > label in that case, which unlocks the net_family table and returns
> > err.
> Yeah, I missed that one. Fixed in the new patch.
>
> > 2) Bigger issue, why not attach the owner to struct sock
> > instead of socket? The sock can exist, and thus reference
> > the protocol family code, long after the socket (ie. the
> > user end) is killed off and closed.
> >
> > For example, this could happen for just about any protocol family
> > due to stray device sk_buff references to the sock and thus the
> > protocol family.
> Good point. Alghough generic socket code does not necessarily reference
> proto family module via struct sock. Only in case when family installed
> non default callbacks (sk->dataready, sk->destruct, etc). Some families
> (af_ipx for example) don't. But I think it's a good idea to refcount
> struct sock anyway.
>
> Ok. Here is the new patch.
> We still need owner field in struct socket.
>
> # This is a BitKeeper generated patch for the following project:
> # Project Name: Linux kernel tree
> # This patch format is intended for GNU patch command version 2.5 or higher.
> # This patch includes the following deltas:
> # ChangeSet 1.889 -> 1.890
> # net/socket.c 1.39 -> 1.40
> # include/linux/net.h 1.7 -> 1.8
> # include/net/sock.h 1.29 -> 1.30
> # net/core/sock.c 1.14 -> 1.15
> #
> # The following is the BitKeeper ChangeSet Log
> # --------------------------------------------
> # 02/12/25 maxk@qualcomm.com 1.890
> # Convert generic socket code to the new module refcounting API.
> # --------------------------------------------
> #
> diff -Nru a/include/linux/net.h b/include/linux/net.h
> --- a/include/linux/net.h Wed Dec 25 23:29:28 2002
> +++ b/include/linux/net.h Wed Dec 25 23:29:28 2002
> @@ -76,6 +76,8 @@
>
> short type;
> unsigned char passcred;
> +
> + struct module *owner;
> };
>
> struct scm_cookie;
> @@ -124,6 +126,8 @@
> short authentication;
> short encryption;
> short encrypt_net;
> +
> + struct module *owner;
> };
>
> struct net_proto
> diff -Nru a/include/net/sock.h b/include/net/sock.h
> --- a/include/net/sock.h Wed Dec 25 23:29:28 2002
> +++ b/include/net/sock.h Wed Dec 25 23:29:28 2002
> @@ -41,6 +41,7 @@
> #include <linux/config.h>
> #include <linux/timer.h>
> #include <linux/cache.h>
> +#include <linux/module.h>
>
> #include <linux/netdevice.h>
> #include <linux/skbuff.h> /* struct sk_buff */
> @@ -196,7 +197,9 @@
>
> /* RPC layer private data */
> void *user_data;
> -
> +
> + struct module *owner;
> +
> /* Callbacks */
> void (*state_change)(struct sock *sk);
> void (*data_ready)(struct sock *sk,int bytes);
> @@ -577,6 +580,9 @@
>
> static inline void sock_graft(struct sock *sk, struct socket *parent)
> {
> + try_module_get(parent->owner);
> + sk->owner = parent->owner;
> +
> write_lock_bh(&sk->callback_lock);
> sk->sleep = &parent->wait;
> parent->sk = sk;
> diff -Nru a/net/core/sock.c b/net/core/sock.c
> --- a/net/core/sock.c Wed Dec 25 23:29:28 2002
> +++ b/net/core/sock.c Wed Dec 25 23:29:28 2002
> @@ -601,6 +601,7 @@
> sock_lock_init(sk);
> }
> sk->slab = slab;
> + sk->owner = NULL;
> }
>
> return sk;
> @@ -626,6 +627,8 @@
> if (atomic_read(&sk->omem_alloc))
> printk(KERN_DEBUG "sk_free: optmem leakage (%d bytes) detected.\n", atomic_read(&sk->omem_alloc));
>
> + module_put(sk->owner);
> +
> kmem_cache_free(sk->slab, sk);
> }
>
> @@ -1084,10 +1087,10 @@
> sk->zapped = 1;
> sk->socket = sock;
>
> - if(sock)
> - {
> + if (sock) {
> sk->type = sock->type;
> sk->sleep = &sock->wait;
> + sk->owner = sock->owner;
> sock->sk = sk;
> } else
> sk->sleep = NULL;
> diff -Nru a/net/socket.c b/net/socket.c
> --- a/net/socket.c Wed Dec 25 23:29:28 2002
> +++ b/net/socket.c Wed Dec 25 23:29:28 2002
> @@ -470,6 +470,8 @@
>
> sock = SOCKET_I(inode);
>
> + sock->owner = NULL;
> +
> inode->i_mode = S_IFSOCK|S_IRWXUGO;
> inode->i_sock = 1;
> inode->i_uid = current->fsuid;
> @@ -964,8 +966,9 @@
>
> int sock_create(int family, int type, int protocol, struct socket **res)
> {
> - int i;
> + struct net_proto_family *npf;
> struct socket *sock;
> + int err;
>
> /*
> * Check protocol is in range
> @@ -990,14 +993,8 @@
> }
>
> #if defined(CONFIG_KMOD) && defined(CONFIG_NET)
> - /* Attempt to load a protocol module if the find failed.
> - *
> - * 12/09/1996 Marcin: But! this makes REALLY only sense, if the user
> - * requested real, full-featured networking support upon configuration.
> - * Otherwise module support will break!
> - */
> - if (net_families[family]==NULL)
> - {
> + /* Attempt to load a protocol module if the find failed. */
> + if (net_families[family]==NULL) {
> char module_name[30];
> sprintf(module_name,"net-pf-%d",family);
> request_module(module_name);
> @@ -1005,29 +1002,31 @@
> #endif
>
> net_family_read_lock();
> - if (net_families[family] == NULL) {
> - i = -EAFNOSUPPORT;
> - goto out;
> - }
>
> -/*
> - * Allocate the socket and allow the family to set things up. if
> - * the protocol is 0, the family is instructed to select an appropriate
> - * default.
> - */
> + npf = net_families[family];
> + if (!npf || !try_module_get(npf->owner)) {
> + net_family_read_unlock();
> + return -EAFNOSUPPORT;
> + }
> +
> + /*
> + * Allocate the socket and allow the family to set things up. if
> + * the protocol is 0, the family is instructed to select an appropriate
> + * default.
> + */
>
> - if (!(sock = sock_alloc()))
> - {
> + sock = sock_alloc();
> + if (!sock) {
> printk(KERN_WARNING "socket: no more sockets\n");
> - i = -ENFILE; /* Not exactly a match, but its the
> + err = -ENFILE; /* Not exactly a match, but its the
> closest posix thing */
> goto out;
> }
>
> sock->type = type;
> + sock->owner = npf->owner;
>
> - if ((i = net_families[family]->create(sock, protocol)) < 0)
> - {
> + if ((err = npf->create(sock, protocol)) < 0) {
> sock_release(sock);
> goto out;
> }
> @@ -1036,7 +1035,9 @@
>
> out:
> net_family_read_unlock();
> - return i;
> + if (err)
> + module_put(npf->owner);
> + return err;
> }
>
> asmlinkage long sys_socket(int family, int type, int protocol)
> @@ -1198,9 +1199,10 @@
> if (!(newsock = sock_alloc()))
> goto out_put;
>
> - newsock->type = sock->type;
> - newsock->ops = sock->ops;
> -
> + newsock->type = sock->type;
> + newsock->ops = sock->ops;
> + newsock->owner = sock->owner;
> +
> err = sock->ops->accept(sock, newsock, sock->file->f_flags);
> if (err < 0)
> goto out_release;
>
> --
>
> Max
>
>
>

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