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Message-ID: <2025050908-CVE-2025-37835-546f@gregkh>
Date: Fri, 9 May 2025 08:40:09 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-37835: smb: client: Fix netns refcount imbalance causing leaks and use-after-free
From: Greg Kroah-Hartman <gregkh@...nel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
smb: client: Fix netns refcount imbalance causing leaks and use-after-free
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
The Linux kernel CVE team has assigned CVE-2025-37835 to this issue.
Affected and fixed versions
===========================
Issue introduced in 6.6.62 with commit e8c71494181153a134c96da28766a57bd1eac8cb and fixed in 6.6.87 with commit c6b6b8dcef4adf8ee4e439bb97e74106096c71b8
Issue introduced in 6.12 with commit ef7134c7fc48e1441b398e55a862232868a6f0a7 and fixed in 6.12.23 with commit 7d8dfc27d90d41627c0d6ada97ed0ab57b3dae25
Issue introduced in 6.12 with commit ef7134c7fc48e1441b398e55a862232868a6f0a7 and fixed in 6.13.11 with commit 961755d0055e0e96d1849cc0425da966c8a64e53
Issue introduced in 6.12 with commit ef7134c7fc48e1441b398e55a862232868a6f0a7 and fixed in 6.14.2 with commit 476617a4ca0123f0df677d547a82a110c27c8c74
Issue introduced in 6.12 with commit ef7134c7fc48e1441b398e55a862232868a6f0a7 and fixed in 6.15-rc1 with commit 4e7f1644f2ac6d01dc584f6301c3b1d5aac4eaef
Issue introduced in 6.11.9 with commit c7f9282fc27fc36dbaffc8527c723de264a132f8
Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.
Unaffected versions might change over time as fixes are backported to
older supported kernel versions. The official CVE entry at
https://cve.org/CVERecord/?id=CVE-2025-37835
will be updated if fixes are backported, please check that for the most
up to date information about this issue.
Affected files
==============
The file(s) affected by this issue are:
fs/smb/client/connect.c
Mitigation
==========
The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes. Individual
changes are never tested alone, but rather are part of a larger kernel
release. Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all. If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
https://git.kernel.org/stable/c/c6b6b8dcef4adf8ee4e439bb97e74106096c71b8
https://git.kernel.org/stable/c/7d8dfc27d90d41627c0d6ada97ed0ab57b3dae25
https://git.kernel.org/stable/c/961755d0055e0e96d1849cc0425da966c8a64e53
https://git.kernel.org/stable/c/476617a4ca0123f0df677d547a82a110c27c8c74
https://git.kernel.org/stable/c/4e7f1644f2ac6d01dc584f6301c3b1d5aac4eaef
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