Re: [PATCH V2] scsi: iscsi_tcp: Fix use-after-free when do get_host_param

Wu Bo <wubo40@xxxxxxxxxx> · Tue, 23 Mar 2021 09:19:14 +0800

On 2021/3/22 4:21, michael.christie@xxxxxxxxxx wrote:
On 3/21/21 1:47 AM, Wu Bo wrote:
From: Wu Bo <wubo40@xxxxxxxxxx>

iscsid(cpu1): Logout of iscsi session, will do destroy session,
tcp_sw_host->session is not set to NULL before release the iscsi session.
in the iscsi_sw_tcp_session_destroy().

iscsadm(cpu2): Get host parameters access to tcp_sw_host->session in the
iscsi_sw_tcp_host_get_param(), tcp_sw_host->session is not NULL,
but pointed to a freed space.

Add ihost->lock and kref to protect the session,
between get host parameters and destroy iscsi session.

[29844.848044] sd 2:0:0:1: [sdj] Synchronizing SCSI cache
[29844.923745] scsi 2:0:0:1: alua: Detached
[29844.927840] ==================================================================
[29844.927861] BUG: KASAN: use-after-free in iscsi_sw_tcp_host_get_param+0xf4/0x218 [iscsi_tcp]
[29844.927864] Read of size 8 at addr ffff80002c0b8f68 by task iscsiadm/523945
[29844.927871] CPU: 1 PID: 523945 Comm: iscsiadm Kdump: loaded Not tainted 4.19.90.kasan.aarch64
[29844.927873] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
[29844.927875] Call trace:
[29844.927884]  dump_backtrace+0x0/0x270
[29844.927886]  show_stack+0x24/0x30
[29844.927895]  dump_stack+0xc4/0x120
[29844.927902]  print_address_description+0x68/0x278
[29844.927904]  kasan_report+0x20c/0x338
[29844.927906]  __asan_load8+0x88/0xb0
[29844.927910]  iscsi_sw_tcp_host_get_param+0xf4/0x218 [iscsi_tcp]
[29844.927932]  show_host_param_ISCSI_HOST_PARAM_IPADDRESS+0x84/0xa0 [scsi_transport_iscsi]
[29844.927938]  dev_attr_show+0x48/0x90
[29844.927943]  sysfs_kf_seq_show+0x100/0x1e0
[29844.927946]  kernfs_seq_show+0x88/0xa0
[29844.927949]  seq_read+0x164/0x748
[29844.927951]  kernfs_fop_read+0x204/0x308
[29844.927956]  __vfs_read+0xd4/0x2d8
[29844.927958]  vfs_read+0xa8/0x198
[29844.927960]  ksys_read+0xd0/0x180
[29844.927962]  __arm64_sys_read+0x4c/0x60
[29844.927966]  el0_svc_common+0xa8/0x230
[29844.927969]  el0_svc_handler+0xdc/0x138
[29844.927971]  el0_svc+0x10/0x218

[29844.928063] Freed by task 53358:
[29844.928066]  __kasan_slab_free+0x120/0x228
[29844.928068]  kasan_slab_free+0x10/0x18
[29844.928069]  kfree+0x98/0x278
[29844.928083]  iscsi_session_release+0x84/0xa0 [scsi_transport_iscsi]
[29844.928085]  device_release+0x4c/0x100
[29844.928089]  kobject_put+0xc4/0x288
[29844.928091]  put_device+0x24/0x30
[29844.928105]  iscsi_free_session+0x60/0x70 [scsi_transport_iscsi]
[29844.928112]  iscsi_session_teardown+0x134/0x158 [libiscsi]
[29844.928116]  iscsi_sw_tcp_session_destroy+0x7c/0xd8 [iscsi_tcp]
[29844.928129]  iscsi_if_rx+0x1538/0x1f00 [scsi_transport_iscsi]
[29844.928131]  netlink_unicast+0x338/0x3c8
[29844.928133]  netlink_sendmsg+0x51c/0x588
[29844.928135]  sock_sendmsg+0x74/0x98
[29844.928137]  ___sys_sendmsg+0x434/0x470
[29844.928139]  __sys_sendmsg+0xd4/0x148
[29844.928141]  __arm64_sys_sendmsg+0x50/0x60
[29844.928143]  el0_svc_common+0xa8/0x230
[29844.928146]  el0_svc_handler+0xdc/0x138
[29844.928147]  el0_svc+0x10/0x218
[29844.928148]
[29844.928150] The buggy address belongs to the object at ffff80002c0b8880#012 which belongs to the cache kmalloc-2048 of size 2048
[29844.928153] The buggy address is located 1768 bytes inside of#012 2048-byte region [ffff80002c0b8880, ffff80002c0b9080)
[29844.928154] The buggy address belongs to the page:
[29844.928158] page:ffff7e0000b02e00 count:1 mapcount:0 mapping:ffff8000d8402600 index:0x0 compound_mapcount: 0
[29844.928902] flags: 0x7fffe0000008100(slab|head)
[29844.929215] raw: 07fffe0000008100 ffff7e0003535e08 ffff7e00024a9408 ffff8000d8402600
[29844.929217] raw: 0000000000000000 00000000000f000f 00000001ffffffff 0000000000000000
[29844.929219] page dumped because: kasan: bad access detected
[29844.929219]
[29844.929221] Memory state around the buggy address:
[29844.929223]  ffff80002c0b8e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[29844.929225]  ffff80002c0b8e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[29844.929227] >ffff80002c0b8f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[29844.929228]                                                           ^
[29844.929230]  ffff80002c0b8f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[29844.929232]  ffff80002c0b9000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[29844.929232] ==================================================================
[29844.929234] Disabling lock debugging due to kernel taint
[29844.969534] scsi host2: iSCSI Initiator over TCP/IP

Fixes: a79af8a64d39 ("[SCSI] iscsi_tcp: use iscsi_conn_get_addr_param libiscsi function")
Signed-off-by: Wu Bo <wubo40@xxxxxxxxxx>
Signed-off-by: WenChao Hao <haowenchao@xxxxxxxxxx>
---
  drivers/scsi/iscsi_tcp.c | 23 +++++++++++++++++++++--
  1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c
index 93ce990..579aa80 100644
--- a/drivers/scsi/iscsi_tcp.c
+++ b/drivers/scsi/iscsi_tcp.c
@@ -783,22 +783,32 @@ static int iscsi_sw_tcp_host_get_param(struct Scsi_Host *shost,
  				       enum iscsi_host_param param, char *buf)
  {
  	struct iscsi_sw_tcp_host *tcp_sw_host = iscsi_host_priv(shost);
-	struct iscsi_session *session = tcp_sw_host->session;
+	struct iscsi_session *session;
+	struct iscsi_host *ihost = shost_priv(shost);
  	struct iscsi_conn *conn;
  	struct iscsi_tcp_conn *tcp_conn;
  	struct iscsi_sw_tcp_conn *tcp_sw_conn;
  	struct sockaddr_in6 addr;
+	unsigned long flags;
  	int rc;
  
  	switch (param) {
  	case ISCSI_HOST_PARAM_IPADDRESS:
-		if (!session)
+		spin_lock_irqsave(&ihost->lock, flags);
+		session = tcp_sw_host->session;
+		if (!session) {
+			spin_unlock_irqrestore(&ihost->lock, flags);
  			return -ENOTCONN;
+		}
+
+		get_device(&(session->cls_session->dev));
+		spin_unlock_irqrestore(&ihost->lock, flags);
  
  		spin_lock_bh(&session->frwd_lock);
  		conn = session->leadconn;
  		if (!conn) {
  			spin_unlock_bh(&session->frwd_lock);
+			put_device(&(session->cls_session->dev));
  			return -ENOTCONN;
  		}
  		tcp_conn = conn->dd_data;
@@ -806,12 +816,14 @@ static int iscsi_sw_tcp_host_get_param(struct Scsi_Host *shost,
  		tcp_sw_conn = tcp_conn->dd_data;
  		if (!tcp_sw_conn->sock) {
  			spin_unlock_bh(&session->frwd_lock);
+			put_device(&(session->cls_session->dev));
  			return -ENOTCONN;
  		}
  
  		rc = kernel_getsockname(tcp_sw_conn->sock,
  					(struct sockaddr *)&addr);
  		spin_unlock_bh(&session->frwd_lock);
+		put_device(&(session->cls_session->dev));
  		if (rc < 0)
  			return rc;
  
@@ -901,10 +913,17 @@ static void iscsi_sw_tcp_session_destroy(struct iscsi_cls_session *cls_session)
  {
  	struct Scsi_Host *shost = iscsi_session_to_shost(cls_session);
  	struct iscsi_session *session = cls_session->dd_data;
+	struct iscsi_sw_tcp_host *tcp_sw_host = iscsi_host_priv(shost);
+	struct iscsi_host *ihost = shost_priv(shost);
+	unsigned long flags;
  
  	if (WARN_ON_ONCE(session->leadconn))
  		return;
  
+	spin_lock_irqsave(&ihost->lock, flags);
+	tcp_sw_host->session = NULL;
+	spin_unlock_irqrestore(&ihost->lock, flags);
+
  	iscsi_tcp_r2tpool_free(cls_session->dd_data);
  	iscsi_session_teardown(cls_session);
  

We are tearing down the structs in the wrong order. I think sysfs removal
functions will wait for users accessing the object, so we can do:

1. remove session from sysfs (iscsi_remove_session)
2. remove host from syfs (iscsi_host_remove)

At this point we userspace is not accessing the host and session structs so
we can start to tear them down.

3. free session: iscsi_tcp_r2tpool_free, a modified iscsi_session_teardown
that only does iscsi_free_session instead of iscsi_destroy_session.
4. free host (iscsi_host_free).

Before the device_del function waited for userspace to release refcounts
for sysfs accesses we could have also moved some of thise to a release function.


Hi,

Thank you for your suggestion, I will try to modify tearing down the 
structs order and send the V3 version after testing.

Thanks.








