Описание
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix TCP timers deadlock after rmmod
Commit ef7134c7fc48 ("smb: client: Fix use-after-free of network namespace.") fixed a netns UAF by manually enabled socket refcounting (sk->sk_net_refcnt=1 and sock_inuse_add(net, 1)).
The reason the patch worked for that bug was because we now hold references to the netns (get_net_track() gets a ref internally) and they're properly released (internally, on __sk_destruct()), but only because sk->sk_net_refcnt was set.
Problem: (this happens regardless of CONFIG_NET_NS_REFCNT_TRACKER and regardless if init_net or other)
Setting sk->sk_net_refcnt=1 manually and after socket creation is not only out of cifs scope, but also technically wrong -- it's set conditionally based on user (=1) vs kernel (=0) sockets. And net/ implementations seem to base their user vs kernel space operations on it.
e.g. upon TCP socket close, the TCP timers are not cleared because sk->...
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix TCP timers deadlock after rmmod
Commit ef7134c7fc48 ("smb: client: Fix use-after-free of network namespace.") fixed a netns UAF by manually enabled socket refcounting (sk->sk_net_refcnt=1 and sock_inuse_add(net, 1)).
The reason the patch worked for that bug was because we now hold references to the netns (get_net_track() gets a ref internally) and they're properly released (internally, on __sk_destruct()), but only because sk->sk_net_refcnt was set.
Problem: (this happens regardless of CONFIG_NET_NS_REFCNT_TRACKER and regardless if init_net or other)
Setting sk->sk_net_refcnt=1 manually and after socket creation is not only out of cifs scope, but also technically wrong -- it's set conditionally based on user (=1) vs kernel (=0) sockets. And net/ implementations seem to base their user vs kernel space operations on it.
e.g. upon TCP socket close, the TCP timers are not cleared because sk->sk_net_refcnt=1: (cf. commit 151c9c724d05 ("tcp: properly terminate timers for kernel sockets"))
net/ipv4/tcp.c: void tcp_close(struct sock *sk, long timeout) { lock_sock(sk); __tcp_close(sk, timeout); release_sock(sk); if (!sk->sk_net_refcnt) inet_csk_clear_xmit_timers_sync(sk); sock_put(sk); }
Which will throw a lockdep warning and then, as expected, deadlock on tcp_write_timer().
A way to reproduce this is by running the reproducer from ef7134c7fc48 and then 'rmmod cifs'. A few seconds later, the deadlock/lockdep warning shows up.
Fix: We shouldn't mess with socket internals ourselves, so do not set sk_net_refcnt manually.
Also change __sock_create() to sock_create_kern() for explicitness.
As for non-init_net network namespaces, we deal with it the best way we can -- hold an extra netns reference for server->ssocket and drop it when it's released. This ensures that the netns still exists whenever we need to create/destroy server->ssocket, but is not directly tied to it.
Связанные уязвимости
[REJECTED CVE] A vulnerability was suspected in the Linux kernel's SMB client module related to TCP timers and potential deadlocks after module removal (rmmod cifs). The issue stemmed from incorrect manual manipulation of sk->sk_net_refcnt, which led to TCP timers not being properly cleared, causing lockdep warnings and deadlocks. However, this was an internal kernel misconfiguration affecting cleanup behavior rather than a security flaw exploitable by an attacker. Since no privilege escalation or data exposure was possible, this does not qualify as a security vulnerability.
Rejected reason: This CVE ID has been rejected or withdrawn by its CVE Numbering Authority.
