Re: [PATCH net v2] sunrpc: fix one UAF issue caused by sunrpc kernel tcp socket

"liujian (CE)" <liujian56@xxxxxxxxxx> · Thu, 7 Nov 2024 20:03:40 +0800

在 2024/11/3 12:09, Kuniyuki Iwashima 写道:
From: Liu Jian <liujian56@xxxxxxxxxx>
Date: Wed, 30 Oct 2024 17:49:53 +0800
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.

To fix this problem:
Add the sock_create_kern_getnet() helper function, add the get_net()
  operation for the kernel socket.

Fixes: 26abe14379f8 ("net: Modify sk_alloc to not reference count the netns of kernel sockets.")
Signed-off-by: Liu Jian <liujian56@xxxxxxxxxx>
---
v1: https://lore.kernel.org/all/20241024015543.568476-1-liujian56@xxxxxxxxxx/
v1->v2: change to get netns reference count.
  include/linux/net.h   |  1 +
  net/socket.c          | 28 ++++++++++++++++++++++++++++
  net/sunrpc/svcsock.c  |  2 +-
  net/sunrpc/xprtsock.c |  2 +-
  4 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/include/linux/net.h b/include/linux/net.h
index b75bc534c1b3..58216da3b62c 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -255,6 +255,7 @@ int __sock_create(struct net *net, int family, int type, int proto,
  		  struct socket **res, int kern);
  int sock_create(int family, int type, int proto, struct socket **res);
  int sock_create_kern(struct net *net, int family, int type, int proto, struct socket **res);
+int sock_create_kern_getnet(struct net *net, int family, int type, int proto, struct socket **res);
  int sock_create_lite(int family, int type, int proto, struct socket **res);
  struct socket *sock_alloc(void);
  void sock_release(struct socket *sock);
diff --git a/net/socket.c b/net/socket.c
index 042451f01c65..e64a02445b1a 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1651,6 +1651,34 @@ int sock_create_kern(struct net *net, int family, int type, int protocol, struct
  }
  EXPORT_SYMBOL(sock_create_kern);
  
+int sock_create_kern_getnet(struct net *net, int family, int type, int proto, struct socket **res)
+{
+	struct sock *sk;
+	int ret;
+
+	if (!maybe_get_net(net))
+		return -EINVAL;

Is this really safe ?

IIUC, maybe_get_net() is safe for a net only when it is fetched under
RCU, then rcu_read_lock() prevents cleanup_net() from reusing the net
by rcu_barrier().

Otherwise, there should be a small chance that the same slab object is
reused for another netns between fetching the net and reaching here.

svc_create_socket() is called much later after the netns is fetched,
and _svc_xprt_create() calls try_module_get() before ->xpo_create().
So, it seems the path is not under RCU and maybe_get_net() must be
called much earlier by each call site.

For this reason, when I write a patch for the same issue in CIFS,
I delayed put_net() to cifsd kthread so that the netns refcnt taken
for each CIFS server info lives until the last __sock_create() attempt
from cifsd.

https://lore.kernel.org/linux-cifs/20241102212438.76691-1-kuniyu@xxxxxxxxxx/

Okay, got it. thank you.
Looking at the nfs and nfsd processing flow, it seems that the call to 
__sock_create() to create a TCP socket is always after the mount 
operation get_net(). So it should be fine to use get_net() directly. So 
here I'm going to change may_get_net() to get_net(), move 
sock_create_kern_getnet() to the sunrpc module, and rename it to 
something more appropriate. Is that okay?

+
+	ret = sock_create_kern(net, family, type, proto, res);
+	if (ret < 0) {
+		put_net(net);
+		return ret;
+	}
+
+	sk = (*res)->sk;
+	lock_sock(sk);
+	/* Update ns_tracker to current stack trace and refcounted tracker */
+	__netns_tracker_free(net, &sk->ns_tracker, false);
+
+	sk->sk_net_refcnt = 1;
+	netns_tracker_alloc(net, &sk->ns_tracker, GFP_KERNEL);
+	sock_inuse_add(net, 1);
+	release_sock(sk);
+
+	return ret;
+}
+EXPORT_SYMBOL(sock_create_kern_getnet);
+
  static struct socket *__sys_socket_create(int family, int type, int protocol)
  {
  	struct socket *sock;
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 825ec5357691..6f272013fd9b 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -1526,7 +1526,7 @@ static struct svc_xprt *svc_create_socket(struct svc_serv *serv,
  		return ERR_PTR(-EINVAL);
  	}
  
-	error = __sock_create(net, family, type, protocol, &sock, 1);
+	error = sock_create_kern_getnet(net, family, type, protocol, &sock);
  	if (error < 0)
  		return ERR_PTR(error);
  
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 110749b85040..f7734ce5eec9 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -1925,7 +1925,7 @@ static struct socket *xs_create_sock(struct rpc_xprt *xprt,
  	struct socket *sock;
  	int err;
  
-	err = __sock_create(xprt->xprt_net, family, type, protocol, &sock, 1);
+	err = sock_create_kern_getnet(xprt->xprt_net, family, type, protocol, &sock);
  	if (err < 0) {
  		dprintk("RPC:       can't create %d transport socket (%d).\n",
  				protocol, -err);
--
2.34.1








