Re: [PATCH net] sunrpc: fix one UAF issue caused by sunrpc kernel tcp socket

[Trond Myklebust <trondmy@hammerspace.com>]

On Thu, 2024-10-24 at 02:20 +0000, Trond Myklebust wrote:
> On Thu, 2024-10-24 at 09:55 +0800, Liu Jian wrote:
> > BUG: KASAN: slab-use-after-free in
> > tcp_write_timer_handler+0x156/0x3e0
> > Read of size 1 at addr ffff888111f322cd by task swapper/0/0
> > 
> > CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.12.0-rc4-dirty
> > #7
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-
> > 1
> > Call Trace:
> >  <IRQ>
> >  dump_stack_lvl+0x68/0xa0
> >  print_address_description.constprop.0+0x2c/0x3d0
> >  print_report+0xb4/0x270
> >  kasan_report+0xbd/0xf0
> >  tcp_write_timer_handler+0x156/0x3e0
> >  tcp_write_timer+0x66/0x170
> >  call_timer_fn+0xfb/0x1d0
> >  __run_timers+0x3f8/0x480
> >  run_timer_softirq+0x9b/0x100
> >  handle_softirqs+0x153/0x390
> >  __irq_exit_rcu+0x103/0x120
> >  irq_exit_rcu+0xe/0x20
> >  sysvec_apic_timer_interrupt+0x76/0x90
> >  </IRQ>
> >  <TASK>
> >  asm_sysvec_apic_timer_interrupt+0x1a/0x20
> > RIP: 0010:default_idle+0xf/0x20
> > Code: 4c 01 c7 4c 29 c2 e9 72 ff ff ff 90 90 90 90 90 90 90 90 90
> > 90
> > 90 90
> >  90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 33 f8 25 00 fb f4 <fa> c3
> > cc
> > cc cc
> >  cc 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90
> > RSP: 0018:ffffffffa2007e28 EFLAGS: 00000242
> > RAX: 00000000000f3b31 RBX: 1ffffffff4400fc7 RCX: ffffffffa09c3196
> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff9f00590f
> > RBP: 0000000000000000 R08: 0000000000000001 R09: ffffed102360835d
> > R10: ffff88811b041aeb R11: 0000000000000001 R12: 0000000000000000
> > R13: ffffffffa202d7c0 R14: 0000000000000000 R15: 00000000000147d0
> >  default_idle_call+0x6b/0xa0
> >  cpuidle_idle_call+0x1af/0x1f0
> >  do_idle+0xbc/0x130
> >  cpu_startup_entry+0x33/0x40
> >  rest_init+0x11f/0x210
> >  start_kernel+0x39a/0x420
> >  x86_64_start_reservations+0x18/0x30
> >  x86_64_start_kernel+0x97/0xa0
> >  common_startup_64+0x13e/0x141
> >  </TASK>
> > 
> > Allocated by task 595:
> >  kasan_save_stack+0x24/0x50
> >  kasan_save_track+0x14/0x30
> >  __kasan_slab_alloc+0x87/0x90
> >  kmem_cache_alloc_noprof+0x12b/0x3f0
> >  copy_net_ns+0x94/0x380
> >  create_new_namespaces+0x24c/0x500
> >  unshare_nsproxy_namespaces+0x75/0xf0
> >  ksys_unshare+0x24e/0x4f0
> >  __x64_sys_unshare+0x1f/0x30
> >  do_syscall_64+0x70/0x180
> >  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> > 
> > Freed by task 100:
> >  kasan_save_stack+0x24/0x50
> >  kasan_save_track+0x14/0x30
> >  kasan_save_free_info+0x3b/0x60
> >  __kasan_slab_free+0x54/0x70
> >  kmem_cache_free+0x156/0x5d0
> >  cleanup_net+0x5d3/0x670
> >  process_one_work+0x776/0xa90
> >  worker_thread+0x2e2/0x560
> >  kthread+0x1a8/0x1f0
> >  ret_from_fork+0x34/0x60
> >  ret_from_fork_asm+0x1a/0x30
> > 
> > Reproduction script:
> > 
> > mkdir -p /mnt/nfsshare
> > mkdir -p /mnt/nfs/netns_1
> > mkfs.ext4 /dev/sdb
> > mount /dev/sdb /mnt/nfsshare
> > systemctl restart nfs-server
> > chmod 777 /mnt/nfsshare
> > exportfs -i -o rw,no_root_squash *:/mnt/nfsshare
> > 
> > ip netns add netns_1
> > ip link add name veth_1_peer type veth peer veth_1
> > ifconfig veth_1_peer 11.11.0.254 up
> > ip link set veth_1 netns netns_1
> > ip netns exec netns_1 ifconfig veth_1 11.11.0.1
> > 
> > ip netns exec netns_1 /root/iptables -A OUTPUT -d 11.11.0.254 -p
> > tcp
> > \
> > 	--tcp-flags FIN FIN  -j DROP
> > 
> > (note: In my environment, a DESTROY_CLIENTID operation is always
> > sent
> >  immediately, breaking the nfs tcp connection.)
> > ip netns exec netns_1 timeout -s 9 300 mount -t nfs -o
> > proto=tcp,vers=4.1 \
> > 	11.11.0.254:/mnt/nfsshare /mnt/nfs/netns_1
> > 
> > ip netns del netns_1
> > 
> > The reason here is that the tcp socket in netns_1 (nfs side) has
> > been
> > shutdown and closed (done in xs_destroy), but the FIN message (with
> > ack)
> > is discarded, and the nfsd side keeps sending retransmission
> > messages.
> > As a result, when the tcp sock in netns_1 processes the received
> > message,
> > it sends the message (FIN message) in the sending queue, and the
> > tcp
> > timer
> > is re-established. When the network namespace is deleted, the net
> > structure
> > accessed by tcp's timer handler function causes problems.
> > 
> > The modification here aborts the TCP connection directly in
> > xs_destroy().
> > 
> > Fixes: 26abe14379f8 ("net: Modify sk_alloc to not reference count
> > the
> > netns of kernel sockets.")
> > Signed-off-by: Liu Jian <liujian56@huawei.com>
> > ---
> >  net/sunrpc/xprtsock.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > index 0e1691316f42..91ee3484155a 100644
> > --- a/net/sunrpc/xprtsock.c
> > +++ b/net/sunrpc/xprtsock.c
> > @@ -1287,6 +1287,9 @@ static void xs_reset_transport(struct
> > sock_xprt
> > *transport)
> >  	release_sock(sk);
> >  	mutex_unlock(&transport->recv_mutex);
> >  
> > +	if (sk->sk_prot == &tcp_prot)
> > +		tcp_abort(sk, ECONNABORTED);
> 
> We've already called kernel_sock_shutdown(sock, SHUT_RDWR), and we're
> about to close the socket. Why on earth should we need a hack like
> the
> above in order to abort the connection at this point?
> 
> This would appear to be a networking layer bug, and not an RPC level
> problem.
> 

To put this differently: if a use after free can occur in the kernel
when the RPC layer closes a TCP socket and then exits the network
namespace, then can't that occur when a userland application does the
same?

If not, then what prevents it from happening?

> > +
> >  	trace_rpc_socket_close(xprt, sock);
> >  	__fput_sync(filp);
> >  

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com