maillist inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IBNCLL Reference: https://lore.kernel.org/linux-cifs/CAH2r5muqxgPy=n4Aks_k-2goEZmmD10Dx3u3jgOk... --------------------------------------------- Commit ef7134c7fc48 ("smb: client: Fix use-after-free of network namespace.") attempted to fix a netns use-after-free issue by manually adjusting reference counts via sk->sk_net_refcnt and sock_inuse_add(). However, a later commit e9f2517a3e18 ("smb: client: fix TCP timers deadlock after rmmod") pointed out that the approach of manually setting sk->sk_net_refcnt in the first commit was technically incorrect, as sk->sk_net_refcnt should only be set for user sockets. It led to issues like TCP timers not being cleared properly on close. The second commit moved to a model of just holding an extra netns reference for server->ssocket using get_net(), and dropping it when the server is torn down. But there remain some gaps in the get_net()/put_net() balancing added by these commits. The incomplete reference handling in these fixes results in two issues: 1. Netns refcount leaks[1] The problem process is as follows: ``` mount.cifs cifsd cifs_do_mount cifs_mount cifs_mount_get_session cifs_get_tcp_session get_net() /* First get net. */ ip_connect generic_ip_connect /* Try port 445 */ get_net() ->connect() /* Failed */ put_net() generic_ip_connect /* Try port 139 */ get_net() /* Missing matching put_net() for this get_net().*/ cifs_get_smb_ses cifs_negotiate_protocol smb2_negotiate SMB2_negotiate cifs_send_recv wait_for_response cifs_demultiplex_thread cifs_read_from_socket cifs_readv_from_socket cifs_reconnect cifs_abort_connection sock_release(); server->ssocket = NULL; /* Missing put_net() here. */ generic_ip_connect get_net() ->connect() /* Failed */ put_net() sock_release(); server->ssocket = NULL; free_rsp_buf ... clean_demultiplex_info /* It's only called once here. */ put_net() ``` When cifs_reconnect() is triggered, the server->ssocket is released without a corresponding put_net() for the reference acquired in generic_ip_connect() before. it ends up calling generic_ip_connect() again to retry get_net(). After that, server->ssocket is set to NULL in the error path of generic_ip_connect(), and the net count cannot be released in the final clean_demultiplex_info() function. 2. Potential use-after-free The current refcounting scheme can lead to a potential use-after-free issue in the following scenario: ``` cifs_do_mount cifs_mount cifs_mount_get_session cifs_get_tcp_session get_net() /* First get net */ ip_connect generic_ip_connect get_net() bind_socket kernel_bind /* failed */ put_net() /* after out_err_crypto_release label */ put_net() /* after out_err label */ put_net() ``` In the exception handling process where binding the socket fails, the get_net() and put_net() calls are unbalanced, which may cause the server->net reference count to drop to zero and be prematurely released. To address both issues, this patch ties the netns reference counting to the server->ssocket and server lifecycles. The extra reference is now acquired when the server or socket is created, and released when the socket is destroyed or the server is torn down. [1]: https://bugzilla.kernel.org/show_bug.cgi?id=219792 Fixes: ef7134c7fc48 ("smb: client: Fix use-after-free of network namespace.") Fixes: e9f2517a3e18 ("smb: client: fix TCP timers deadlock after rmmod") Conflicts: fs/cifs/connect.c fs/smb/client/connect.c [Conflicts due to fs/cifs move to fs/smb/client] Signed-off-by: Wang Zhaolong <wangzhaolong1@huawei.com> --- fs/cifs/connect.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c index 1c637d369fbb..07b56705bcb0 100644 --- a/fs/cifs/connect.c +++ b/fs/cifs/connect.c @@ -478,6 +478,7 @@ cifs_reconnect(struct TCP_Server_Info *server) server->ssocket->state, server->ssocket->flags); sock_release(server->ssocket); server->ssocket = NULL; + put_net(cifs_net_ns(server)); } server->sequence_number = 0; server->session_estab = false; @@ -3764,8 +3765,12 @@ generic_ip_connect(struct TCP_Server_Info *server) /* * Grab netns reference for the socket. * - * It'll be released here, on error, or in clean_demultiplex_info() upon server - * teardown. + * This reference will be released in several situations: + * - In the failure path before the cifsd is started + * - In the all place where server->socket is released, it is + * also set to NULL. + * - Ultimately in clean_demultiplex_info(), during the final + * teardown. */ get_net(net); @@ -3780,10 +3785,8 @@ generic_ip_connect(struct TCP_Server_Info *server) } rc = bind_socket(server); - if (rc < 0) { - put_net(cifs_net_ns(server)); + if (rc < 0) return rc; - } /* * Eventually check for other socket options to change from @@ -3828,9 +3831,6 @@ generic_ip_connect(struct TCP_Server_Info *server) if (sport == htons(RFC1001_PORT)) rc = ip_rfc1001_connect(server); - if (rc < 0) - put_net(cifs_net_ns(server)); - return rc; } -- 2.34.3