6.12-stable review patch. If anyone has any objections, please let me know.
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From: Wang Zhaolong wangzhaolong1@huawei.com
[ Upstream commit 4e7f1644f2ac6d01dc584f6301c3b1d5aac4eaef ]
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") Signed-off-by: Wang Zhaolong wangzhaolong1@huawei.com Signed-off-by: Steve French stfrench@microsoft.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/smb/client/connect.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c index d327f31b317db..8b8475b4e2627 100644 --- a/fs/smb/client/connect.c +++ b/fs/smb/client/connect.c @@ -316,6 +316,7 @@ cifs_abort_connection(struct TCP_Server_Info *server) server->ssocket->flags); sock_release(server->ssocket); server->ssocket = NULL; + put_net(cifs_net_ns(server)); } server->sequence_number = 0; server->session_estab = false; @@ -3138,8 +3139,12 @@ 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 thread 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);
@@ -3155,10 +3160,8 @@ 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 @@ -3204,9 +3207,6 @@ 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; }