Re: [PATCH v1 net-next 4/6] socket: Remove kernel socket conversion except for net/rds/.

[Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>]

From: Paolo Abeni <pabeni@xxxxxxxxxx>
Date: Thu, 22 May 2025 10:55:47 +0200
> On 5/17/25 5:50 AM, Kuniyuki Iwashima wrote:
> > Since commit 26abe14379f8 ("net: Modify sk_alloc to not reference
> > count the netns of kernel sockets."), TCP kernel socket has caused
> > many UAF.
> > 
> > We have converted such sockets to hold netns refcnt, and we have
> > the same pattern in cifs, mptcp, nvme, rds, smc, and sunrpc.
> > 
> >   __sock_create_kern(..., &sock);
> >   sk_net_refcnt_upgrade(sock->sk);
> > 
> > Let's drop the conversion and use sock_create_kern() instead.
> > 
> > The changes for cifs, mptcp, nvme, and smc are straightforward.
> > 
> > For sunrpc, we call sock_create_net() for IPPROTO_TCP only and still
> > call __sock_create_kern() for others.
> > 
> > For rds, we cannot drop sk_net_refcnt_upgrade() for accept()ed
> > sockets.
> > 
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> 
> This LGTM, but is touching a few other subsystems, it would be great to
> collect acks from the relevant maintainers: I'm adding a few CCs.
> 
> Direct link to the series:
> 
> https://lore.kernel.org/all/20250517035120.55560-1-kuniyu@xxxxxxxxxx/#t
> 
> > diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c
> > index 37a2ba38f10e..c7b4f5a7cca1 100644
> > --- a/fs/smb/client/connect.c
> > +++ b/fs/smb/client/connect.c
> > @@ -3348,21 +3348,14 @@ generic_ip_connect(struct TCP_Server_Info *server)
> >  		socket = server->ssocket;
> >  	} else {
> >  		struct net *net = cifs_net_ns(server);
> > -		struct sock *sk;
> >  
> > -		rc = __sock_create_kern(net, sfamily, SOCK_STREAM,
> > -					IPPROTO_TCP, &server->ssocket);
> > +		rc = sock_create_kern(net, sfamily, SOCK_STREAM,
> > +				      IPPROTO_TCP, &server->ssocket);
> >  		if (rc < 0) {
> >  			cifs_server_dbg(VFS, "Error %d creating socket\n", rc);
> >  			return rc;
> >  		}
> >  
> > -		sk = server->ssocket->sk;
> > -		__netns_tracker_free(net, &sk->ns_tracker, false);
> > -		sk->sk_net_refcnt = 1;
> > -		get_net_track(net, &sk->ns_tracker, GFP_KERNEL);
> > -		sock_inuse_add(net, 1);
> 
> AFAICS the above implicitly adds a missing net_passive_dec(net), which
> in turns looks like a separate bugfix. What about adding a separate
> patch introducing that line? Could be in the same series to simplify the
> processing.

Thanks for catching!

Will add this patch before this change.

---8<---
commit c7ff005fe4d930169f319aca0bd9577541cd7459 (HEAD)
Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date:   Thu May 22 16:03:29 2025 +0000

    smb: client: Add missing net_passive_dec().
    
    While reverting commit e9f2517a3e18 ("smb: client: fix TCP timers deadlock
    after rmmod"), I should have added net_passive_dec(), which was added between
    the original commit and the revert by commit 5c70eb5c593d ("net: better track
    kernel sockets lifetime").
    
    Let's call net_passive_dec() in generic_ip_connect().
    
    Note that this commit is only needed for 6.14+.
    
    Fixes: 95d2b9f693ff ("Revert "smb: client: fix TCP timers deadlock after rmmod"")
    Cc: <stable@xxxxxxxxxxxxxxx> # 6.14.x
    Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>

diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c
index 37a2ba38f10e..afac23a5a3ec 100644
--- a/fs/smb/client/connect.c
+++ b/fs/smb/client/connect.c
@@ -3359,6 +3359,7 @@ generic_ip_connect(struct TCP_Server_Info *server)
 
                sk = server->ssocket->sk;
                __netns_tracker_free(net, &sk->ns_tracker, false);
+               net_passive_dec(net);
                sk->sk_net_refcnt = 1;
                get_net_track(net, &sk->ns_tracker, GFP_KERNEL);
                sock_inuse_add(net, 1);
---8<---