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c6b6b8dcef
[ 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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.