In the Linux kernel, the following vulnerability has been resolved:
Revert "smb: client: fix TCP timers deadlock after rmmod"
This reverts commit e9f2517a3e18a54a3943c098d2226b245d488801.
Commit e9f2517a3e18 ("smb: client: fix TCP timers deadlock after
rmmod") is intended to fix a null-ptr-deref in LOCKDEP, which is
mentioned as CVE-2024-54680, but is actually did not fix anything;
The issue can be reproduced on top of it. [0]
Also, it reverted the change by commit ef7134c7fc48 ("smb: client:
Fix use-after-free of network namespace.") and introduced a real
issue by reviving the kernel TCP socket.
When a reconnect happens for a CIFS connection, the socket state
transitions to FIN_WAIT_1. Then, inet_csk_clear_xmit_timers_sync()
in tcp_close() stops all timers for the socket.
If an incoming FIN packet is lost, the socket will stay at FIN_WAIT_1
forever, and such sockets could be leaked up to net.ipv4.tcp_max_orphans.
Usually, FIN can be retransmitted by the peer, but if the peer aborts
the connection, the issue comes into reality.
I warned about this privately by pointing out the exact report [1],
but the bogus fix was finally merged.
So, we should not stop the timers to finally kill the connection on
our side in that case, meaning we must not use a kernel socket for
TCP whose sk->sk_net_refcnt is 0.
The kernel socket does not have a reference to its netns to make it
possible to tear down netns without cleaning up every resource in it.
For example, tunnel devices use a UDP socket internally, but we can
destroy netns without removing such devices and let it complete
during exit. Otherwise, netns would be leaked when the last application
died.
However, this is problematic for TCP sockets because TCP has timers to
close the connection gracefully even after the socket is close()d. The
lifetime of the socket and its netns is different from the lifetime of
the underlying connection.
If the socket user does not maintain the netns lifetime, the timer could
be fired after the socket is close()d and its netns is freed up, resulting
in use-after-free.
Actually, we have seen so many similar issues and converted such sockets
to have a reference to netns.
That's why I converted the CIFS client socket to have a reference to
netns (sk->sk_net_refcnt == 1), which is somehow mentioned as out-of-scope
of CIFS and technically wrong in e9f2517a3e18, but **is in-scope and right
fix**.
Regarding the LOCKDEP issue, we can prevent the module unload by
bumping the module refcount when switching the LOCKDDEP key in
sock_lock_init_class_and_name(). [2]
For a while, let's revert the bogus fix.
Note that now we can use sk_net_refcnt_upgrade() for the socket
conversion, but I'll do so later separately to make backport easy.
Metrics
Affected Vendors & Products
No data.
No data.
No data.
References
History
Tue, 29 Apr 2025 19:15:00 +0000
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cvssV3_1
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cvssV3_1
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Fri, 25 Apr 2025 10:30:00 +0000
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Fri, 25 Apr 2025 03:30:00 +0000
| Type | Values Removed | Values Added |
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| Weaknesses | CWE-416 | |
| Metrics |
cvssV3_1
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cvssV3_1
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Tue, 22 Apr 2025 06:45:00 +0000
Tue, 22 Apr 2025 05:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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 counti ---truncated--- | In the Linux kernel, the following vulnerability has been resolved: Revert "smb: client: fix TCP timers deadlock after rmmod" This reverts commit e9f2517a3e18a54a3943c098d2226b245d488801. Commit e9f2517a3e18 ("smb: client: fix TCP timers deadlock after rmmod") is intended to fix a null-ptr-deref in LOCKDEP, which is mentioned as CVE-2024-54680, but is actually did not fix anything; The issue can be reproduced on top of it. [0] Also, it reverted the change by commit ef7134c7fc48 ("smb: client: Fix use-after-free of network namespace.") and introduced a real issue by reviving the kernel TCP socket. When a reconnect happens for a CIFS connection, the socket state transitions to FIN_WAIT_1. Then, inet_csk_clear_xmit_timers_sync() in tcp_close() stops all timers for the socket. If an incoming FIN packet is lost, the socket will stay at FIN_WAIT_1 forever, and such sockets could be leaked up to net.ipv4.tcp_max_orphans. Usually, FIN can be retransmitted by the peer, but if the peer aborts the connection, the issue comes into reality. I warned about this privately by pointing out the exact report [1], but the bogus fix was finally merged. So, we should not stop the timers to finally kill the connection on our side in that case, meaning we must not use a kernel socket for TCP whose sk->sk_net_refcnt is 0. The kernel socket does not have a reference to its netns to make it possible to tear down netns without cleaning up every resource in it. For example, tunnel devices use a UDP socket internally, but we can destroy netns without removing such devices and let it complete during exit. Otherwise, netns would be leaked when the last application died. However, this is problematic for TCP sockets because TCP has timers to close the connection gracefully even after the socket is close()d. The lifetime of the socket and its netns is different from the lifetime of the underlying connection. If the socket user does not maintain the netns lifetime, the timer could be fired after the socket is close()d and its netns is freed up, resulting in use-after-free. Actually, we have seen so many similar issues and converted such sockets to have a reference to netns. That's why I converted the CIFS client socket to have a reference to netns (sk->sk_net_refcnt == 1), which is somehow mentioned as out-of-scope of CIFS and technically wrong in e9f2517a3e18, but **is in-scope and right fix**. Regarding the LOCKDEP issue, we can prevent the module unload by bumping the module refcount when switching the LOCKDDEP key in sock_lock_init_class_and_name(). [2] For a while, let's revert the bogus fix. Note that now we can use sk_net_refcnt_upgrade() for the socket conversion, but I'll do so later separately to make backport easy. |
| Title | smb: client: Fix netns refcount imbalance causing leaks and use-after-free | Revert "smb: client: fix TCP timers deadlock after rmmod" |
| References |
|
Sat, 19 Apr 2025 02:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
| |
| Metrics |
threat_severity
|
cvssV3_1
|
Wed, 16 Apr 2025 14:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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 counti ---truncated--- | |
| Title | smb: client: Fix netns refcount imbalance causing leaks and use-after-free | |
| References |
|
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published: 2025-04-16T14:12:27.882Z
Updated: 2025-04-25T10:06:47.046Z
Reserved: 2024-12-29T08:45:45.815Z
Link: CVE-2025-22077
Vulnrichment
No data.
NVD
Status : Awaiting Analysis
Published: 2025-04-16T15:16:01.907
Modified: 2025-04-25T11:15:45.767
Link: CVE-2025-22077
Redhat