From a79af59efd20990473d579b1d8d70bb120f0920c Mon Sep 17 00:00:00 2001 From: Frank Filz Date: Tue, 27 Sep 2005 15:23:38 -0700 Subject: [PATCH] [NET]: Fix module reference counts for loadable protocol modules I have been experimenting with loadable protocol modules, and ran into several issues with module reference counting. The first issue was that __module_get failed at the BUG_ON check at the top of the routine (checking that my module reference count was not zero) when I created the first socket. When sk_alloc() is called, my module reference count was still 0. When I looked at why sctp didn't have this problem, I discovered that sctp creates a control socket during module init (when the module ref count is not 0), which keeps the reference count non-zero. This section has been updated to address the point Stephen raised about checking the return value of try_module_get(). The next problem arose when my socket init routine returned an error. This resulted in my module reference count being decremented below 0. My socket ops->release routine was also being called. The issue here is that sock_release() calls the ops->release routine and decrements the ref count if sock->ops is not NULL. Since the socket probably didn't get correctly initialized, this should not be done, so we will set sock->ops to NULL because we will not call try_module_get(). While searching for another bug, I also noticed that sys_accept() has a possibility of doing a module_put() when it did not do an __module_get so I re-ordered the call to security_socket_accept(). Signed-off-by: Frank Filz Signed-off-by: David S. Miller --- net/core/sock.c | 20 ++++++++++++-------- net/socket.c | 13 ++++++++----- 2 files changed, 20 insertions(+), 13 deletions(-) diff --git a/net/core/sock.c b/net/core/sock.c index ac63b56e23b2..928d2a1d6d8e 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -660,16 +660,20 @@ struct sock *sk_alloc(int family, unsigned int __nocast priority, sock_lock_init(sk); } - if (security_sk_alloc(sk, family, priority)) { - if (slab != NULL) - kmem_cache_free(slab, sk); - else - kfree(sk); - sk = NULL; - } else - __module_get(prot->owner); + if (security_sk_alloc(sk, family, priority)) + goto out_free; + + if (!try_module_get(prot->owner)) + goto out_free; } return sk; + +out_free: + if (slab != NULL) + kmem_cache_free(slab, sk); + else + kfree(sk); + return NULL; } void sk_free(struct sock *sk) diff --git a/net/socket.c b/net/socket.c index dbd1a6851edd..3145103cdf54 100644 --- a/net/socket.c +++ b/net/socket.c @@ -1145,8 +1145,11 @@ static int __sock_create(int family, int type, int protocol, struct socket **res if (!try_module_get(net_families[family]->owner)) goto out_release; - if ((err = net_families[family]->create(sock, protocol)) < 0) + if ((err = net_families[family]->create(sock, protocol)) < 0) { + sock->ops = NULL; goto out_module_put; + } + /* * Now to bump the refcnt of the [loadable] module that owns this * socket at sock_release time we decrement its refcnt. @@ -1360,16 +1363,16 @@ asmlinkage long sys_accept(int fd, struct sockaddr __user *upeer_sockaddr, int _ newsock->type = sock->type; newsock->ops = sock->ops; - err = security_socket_accept(sock, newsock); - if (err) - goto out_release; - /* * We don't need try_module_get here, as the listening socket (sock) * has the protocol module (sock->ops->owner) held. */ __module_get(newsock->ops->owner); + err = security_socket_accept(sock, newsock); + if (err) + goto out_release; + err = sock->ops->accept(sock, newsock, sock->file->f_flags); if (err < 0) goto out_release; -- 2.20.1