Re: [PATCH 1/2] iscsi_tcp: Fix NULL pointer dereference in iscsi_sw_tcp_conn_get_param()

[Mike Christie <michael.christie@oracle.com>]

On 3/3/22 8:56 PM, Wenchao Hao wrote:
> kernel might crash in iscsi_sw_tcp_conn_get_param() because it dereference
> an invalid address.
> 
> The initialization of iscsi_conn's dd_data is after device_register() of
> struct iscsi_cls_conn, so iscsi_conn's dd_data might not initialized when
> iscsi_sw_tcp_conn_get_param() is called.
> 
> Following stack would be reported and kernel would panic.
> 
> [449311.812887] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
> [449311.812893] Mem abort info:
> [449311.812895]   ESR = 0x96000004
> [449311.812899]   Exception class = DABT (current EL), IL = 32 bits
> [449311.812901]   SET = 0, FnV = 0
> [449311.812903]   EA = 0, S1PTW = 0
> [449311.812905] Data abort info:
> [449311.812907]   ISV = 0, ISS = 0x00000004
> [449311.812909]   CM = 0, WnR = 0
> [449311.812915] user pgtable: 4k pages, 48-bit VAs, pgdp = 00000000e26e7ace
> [449311.812918] [0000000000000008] pgd=0000000000000000
> [449311.812925] Internal error: Oops: 96000004 [#1] SMP
> [449311.814974] Process iscsiadm (pid: 8286, stack limit = 0xffff800010f78000)
> [449311.815570] CPU: 0 PID: 8286 Comm: iscsiadm Kdump: loaded Tainted: G    B   W         4.19.90-vhulk2201.1.0.h1021.kasan.eulerosv2r10.aarch64 #1
> [449311.816584] sd 1:0:0:1: [sdg] Attached SCSI disk
> [449311.816695] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
> [449311.817677] pstate: 40400005 (nZcv daif +PAN -UAO)
> [449311.818121] pc : iscsi_sw_tcp_conn_get_param+0xec/0x300 [iscsi_tcp]
> [449311.818688] lr : iscsi_sw_tcp_conn_get_param+0xe8/0x300 [iscsi_tcp]
> [449311.819244] sp : ffff800010f7f890
> [449311.819542] x29: ffff800010f7f890 x28: ffff8000cb1bea38
> [449311.820025] x27: ffff800010911010 x26: ffff2000028887a4
> [449311.820500] x25: ffff800009200d98 x24: ffff800010911000
> [449311.820973] x23: 0000000000000000 x22: ffff8000cb1bea28
> [449311.821458] x21: 0000000000000015 x20: ffff200081afa000
> [449311.821934] x19: 1ffff000021eff20 x18: 0000000000000000
> [449311.822414] x17: 0000000000000000 x16: ffff200080618220
> [449311.822891] x15: 0000000000000000 x14: 0000000000000000
> [449311.823413] x13: 0000000000000000 x12: 0000000000000000
> [449311.823897] x11: 1ffff0001ab4f41f x10: ffff10001ab4f41f
> [449311.824373] x9 : 0000000000000000 x8 : ffff8000d5a7a100
> [449311.824847] x7 : 0000000000000000 x6 : dfff200000000000
> [449311.825329] x5 : ffff1000021eff20 x4 : ffff8000cb1bea30
> [449311.825806] x3 : ffff200002911178 x2 : ffff2000841ff000
> [449311.826281] x1 : e0c234eab8420c00 x0 : ffff8000cb1bea38
> [449311.826756] Call trace:
> [449311.826987]  iscsi_sw_tcp_conn_get_param+0xec/0x300 [iscsi_tcp]
> [449311.827550]  show_conn_ep_param_ISCSI_PARAM_CONN_ADDRESS+0xe4/0x100 [scsi_transport_iscsi]
> [449311.828304]  dev_attr_show+0x58/0xb0
> [449311.828639]  sysfs_kf_seq_show+0x124/0x210
> [449311.829014]  kernfs_seq_show+0x8c/0xa0
> [449311.829362]  seq_read+0x188/0x8a0
> [449311.829667]  kernfs_fop_read+0x250/0x398
> [449311.830024]  __vfs_read+0xe0/0x350
> [449311.830339]  vfs_read+0xbc/0x1c0
> [449311.830635]  ksys_read+0xdc/0x1b8
> [449311.830941]  __arm64_sys_read+0x50/0x60
> [449311.831295]  el0_svc_common+0xc8/0x320
> [449311.831642]  el0_svc_handler+0xf8/0x160
> [449311.831998]  el0_svc+0x10/0x218
> [449311.832292] Code: f94006d7 910022e0 940007bb aa1c03e0 (f94006f9)
> 
> Signed-off-by: Wenchao Hao <haowenchao@huawei.com>
> Signed-off-by: Wu Bo <wubo40@huawei.com>
> ---
>  drivers/scsi/iscsi_tcp.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c
> index 1bc37593c88f..14db224486be 100644
> --- a/drivers/scsi/iscsi_tcp.c
> +++ b/drivers/scsi/iscsi_tcp.c
> @@ -741,11 +741,16 @@ static int iscsi_sw_tcp_conn_get_param(struct iscsi_cls_conn *cls_conn,
>  {
>  	struct iscsi_conn *conn = cls_conn->dd_data;
>  	struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
> -	struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
> +	struct iscsi_sw_tcp_conn *tcp_sw_conn;
>  	struct sockaddr_in6 addr;
>  	struct socket *sock;
>  	int rc;
>  
> +	if (!tcp_conn)
> +		return -ENOTCONN;
> +
> +	tcp_sw_conn = tcp_conn->dd_data;
> +
>  	switch(param) {
>  	case ISCSI_PARAM_CONN_PORT:
>  	case ISCSI_PARAM_CONN_ADDRESS:

We are actually doing sysfs/device addition wrong.

We should be doing the 2 step setup where in step 1 we alloc/init.
When everything is allocated and initialized, then we should do
device_add which exposes us to sysfs. On the teardown side, we are
then supposed to do 2 steps where the remove function does device_del
which waits until sysfs accesses are completed. We can then tear
the structs down and free them and call device_put.

The exposure to NL would be similar where it goes into the wrapper
around device_add. However, see my comments on the other patch where
I don't think we can hit the bug you mention because every nl cmd
that calls into the drivers is done under the rx_queue_mutex.

I think we should separate the iscsi_create_conn function like we
do for sessions. This is going to be a little more involved because
you need to also convert iscsi_tcp_conn_setup and the drivers since
we can call into the drivers for the get_conn_param callout.