Re: [PATCH/RFC] New module refcounting for net_proto_family

Max Krasnyansky
2002-12-26T21:49:13Z

> 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