Re: [PATCH] ib_isert: prevent NULL pointer dereference in isert_login_recv_done() (was: Re: NULL pointer dereference in isert_login_recv_done in 4.9.32)

[Leon Romanovsky]

On Fri, Jun 23, 2017 at 12:37:57AM +0200, Andrea Righi wrote:
> On Wed, Jun 21, 2017 at 10:33:45AM -0600, Robert LeBlanc wrote:
> > On Wed, Jun 21, 2017 at 9:17 AM, Robert LeBlanc <robert@xxxxxxxxxxxxx> wrote:
> > > On Tue, Jun 20, 2017 at 12:54 PM, Robert LeBlanc <robert@xxxxxxxxxxxxx> wrote:
> > >> We have hit this four times today. Any ideas?
> > >>
> > >> [  169.382113] BUG: unable to handle kernel NULL pointer dereference at           (null)
> > >> [  169.382152] IP: [<ffffffffa051e968>] isert_login_recv_done+0x28/0x170 [ib_isert]
>
> So, we spent more time to track down this bug.
>
> It seems that at login time an error is happening, not sure exactly what
> kind of error, but isert_connect_error() is called and isert_conn->cm_id
> is set to NULL.
>
> Later, isert_login_recv_done() is trying to access
> isert_conn->cm_id->device and we get the NULL pointer dereference.
>
> Following there's the patch that we have applied to track down this
> problem.
>
> And this is what we see in dmesg with this patch applied:
>
>  [  658.633188] isert: isert_connect_error: conn ffff887f2209c000 error
>  [  658.633226] isert: isert_login_recv_done: login with broken rdma_cm_id
>
> As we can see isert_connect_error() is called before isert_login_recv_done
> and at that point isert_conn->cm_id is NULL.
>
> Obviously simply checking if the pointer is NULL, returning and ignoring
> the error in isert_login_recv_done() is not the best fix ever and I'm
> not sure if I'm breaking something else doing so (even if with this
> patch the kernel doesn't crash and I've not seen any problem so far).
>
> Maybe a better way is to tear down the whole connection when this
> particular case is happening? Suggestions?
>
> Thanks,
> -Andrea
>
> ---
> ib_isert: prevent NULL pointer dereference in isert_login_recv_done()
>
> During a login if an error is happening isert_connect_error() is called
> and isert_conn->cm_id is set to NULL.
>
> Later, isert_login_recv_done() is executed, trying to access
> isert_conn->cm_id->device, causing the following BUG:
>
>  [  169.382113] BUG: unable to handle kernel NULL pointer dereference at (null)
>  [  169.382152] IP: [<ffffffffa051e968>] isert_login_recv_done+0x28/0x170 [ib_isert]
>
> Check if isert_con->cm_id is set to NULL in isert_login_recv_done() to
> avoid this problem.
>
> Signed-off-by: Andrea Righi <righi.andrea@xxxxxxxxx>
> Signed-off-by: Robert LeBlanc <robert@xxxxxxxxxxxxx>
> ---
>  drivers/infiniband/ulp/isert/ib_isert.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/infiniband/ulp/isert/ib_isert.c b/drivers/infiniband/ulp/isert/ib_isert.c
> index fcbed35..a8c1143 100644
> --- a/drivers/infiniband/ulp/isert/ib_isert.c
> +++ b/drivers/infiniband/ulp/isert/ib_isert.c
> @@ -741,6 +741,7 @@ isert_connect_error(struct rdma_cm_id *cma_id)
>  {
>  	struct isert_conn *isert_conn = cma_id->qp->qp_context;
>
> +	isert_warn("conn %p error\n", isert_conn);

the same can be achieved with tracing, please don't put it.

>  	list_del_init(&isert_conn->node);
>  	isert_conn->cm_id = NULL;
>  	isert_put_conn(isert_conn);
> @@ -1452,7 +1453,13 @@ static void
>  isert_login_recv_done(struct ib_cq *cq, struct ib_wc *wc)
>  {
>  	struct isert_conn *isert_conn = wc->qp->qp_context;
> -	struct ib_device *ib_dev = isert_conn->cm_id->device;
> +struct ib_device *ib_dev;
> +
> +	if (unlikely(isert_conn->cm_id == NULL)) {

There is no need to explicitly compare with NULL. !isert_conn->cm_id
will do the trick.

Thanks

> +		isert_warn("login with broken rdma_cm_id");
> +		return;
> +	}
> +	ib_dev = isert_conn->cm_id->device;
>
>  	if (unlikely(wc->status != IB_WC_SUCCESS)) {
>  		isert_print_wc(wc, "login recv");
> --
> 2.7.4
> --
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