[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)

[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)

[Andrea Righi]

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@leblancnet.us> wrote:
> > On Tue, Jun 20, 2017 at 12:54 PM, Robert LeBlanc <robert@leblancnet.us> 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@gmail.com>
Signed-off-by: Robert LeBlanc <robert@leblancnet.us>
---
 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);
 	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)) {
+		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

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)

[Nicholas A. Bellinger]

Hi Andrea & Robert,

(Adding HCH CC')

On Fri, 2017-06-23 at 00:37 +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@leblancnet.us> wrote:
> > > On Tue, Jun 20, 2017 at 12:54 PM, Robert LeBlanc <robert@leblancnet.us> 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@gmail.com>
> Signed-off-by: Robert LeBlanc <robert@leblancnet.us>
> ---
>  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);
>  	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)) {
> +		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");

So I assume isert_cma_handler() -> isert_connect_error() getting called
to clear isert_conn->cm_id before connection established, and
subsequently isert_conn->login_req_buf->rx_cqe.done() ->
isert_login_recv_done() still getting invoked after connection failure
is new RDMA API behavior..

That said, following Sagi's original patch that added the clearing of
isert_conn->cm_id to isert_connect_error(), it probably makes sense to
use isert_conn->device->ib_device, and avoid dereferencing
isert_conn->cm_id before connection is established.

Here's a quick (untested) patch to do this for recv/send done callbacks,
and avoid using isert_conn->cm_id during isert_rdma_accept().

Sagi + Co, WDYT..?

diff --git a/drivers/infiniband/ulp/isert/ib_isert.c b/drivers/infiniband/ulp/isert/ib_isert.c
index fcbed35..f7f97f3 100644
--- a/drivers/infiniband/ulp/isert/ib_isert.c
+++ b/drivers/infiniband/ulp/isert/ib_isert.c
@@ -52,7 +52,7 @@
 static int
 isert_login_post_recv(struct isert_conn *isert_conn);
 static int
-isert_rdma_accept(struct isert_conn *isert_conn);
+isert_rdma_accept(struct isert_conn *isert_conn, struct rdma_cm_id *cm_id);
 struct rdma_cm_id *isert_setup_id(struct isert_np *isert_np);
 
 static void isert_release_work(struct work_struct *work);
@@ -543,7 +543,7 @@
 	if (ret)
 		goto out_conn_dev;
 
-	ret = isert_rdma_accept(isert_conn);
+	ret = isert_rdma_accept(isert_conn, cma_id);
 	if (ret)
 		goto out_conn_dev;
 
@@ -1452,7 +1452,7 @@
 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 = isert_conn->device->ib_device;
 
 	if (unlikely(wc->status != IB_WC_SUCCESS)) {
 		isert_print_wc(wc, "login recv");
@@ -1769,7 +1769,7 @@
 isert_login_send_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 = isert_conn->device->ib_device;
 	struct iser_tx_desc *tx_desc = cqe_to_tx_desc(wc->wr_cqe);
 
 	if (unlikely(wc->status != IB_WC_SUCCESS)) {
@@ -2369,9 +2369,8 @@ struct rdma_cm_id *
 }
 
 static int
-isert_rdma_accept(struct isert_conn *isert_conn)
+isert_rdma_accept(struct isert_conn *isert_conn, struct rdma_cm_id *cm_id)
 {
-	struct rdma_cm_id *cm_id = isert_conn->cm_id;
 	struct rdma_conn_param cp;
 	int ret;
 	struct iser_cm_hdr rsp_hdr;

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

[Sagi Grimberg]

> Hi Andrea & Robert,

Hi Andrea, Robert, Nic and Co

>>>>> 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?

That is an accurate analysis of what is going on, good job!

> So I assume isert_cma_handler() -> isert_connect_error() getting called
> to clear isert_conn->cm_id before connection established, and
> subsequently isert_conn->login_req_buf->rx_cqe.done() ->
> isert_login_recv_done() still getting invoked after connection failure
> is new RDMA API behavior..

That is correct, but its not really a new behavior, and absolutely
not introduced by the new RDMA API. We will _always_ see the
completion of _all_ recv wrs posted on the qp (given that we assigned
a ->done handler), this is a FLUSH error completion, we just don't
get to verify that because we deref NULL before.

The issue here, as you indicated was the assumption that dereferencing
the connection cm_id is always safe, which is not true since:

commit 4a579da2586bd3b79b025947ea24ede2bbfede62
Author: Sagi Grimberg <sagig@mellanox.com>
Date:   Sun Mar 29 15:52:04 2015 +0300

     iser-target: Fix possible deadlock in RDMA_CM connection error

     Before we reach to connection established we may get an
     error event. In this case the core won't teardown this
     connection (never established it), so we take care of freeing
     it ourselves.

     Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
     Cc: <stable@vger.kernel.org> # v3.10+
     Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

As I see it, we have a direct reference to the isert_device from
isert_conn which is the one-liner fix that we actually need (like
we do in isert_rdma_read_done, isert_rdma_write_done),  guess we
also need it in isert_login_send_done, isert_send_done (although
it can't really happen, but better safe and consistent than sorry).

> @@ -1452,7 +1452,7 @@
>   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 = isert_conn->device->ib_device;
>   
>   	if (unlikely(wc->status != IB_WC_SUCCESS)) {
>   		isert_print_wc(wc, "login recv");

That's the one...

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)

[Andrea Righi]

On Sun, Jun 25, 2017 at 04:58:04PM -0700, Nicholas A. Bellinger wrote:
...
> So I assume isert_cma_handler() -> isert_connect_error() getting called
> to clear isert_conn->cm_id before connection established, and
> subsequently isert_conn->login_req_buf->rx_cqe.done() ->
> isert_login_recv_done() still getting invoked after connection failure
> is new RDMA API behavior..
> 
> That said, following Sagi's original patch that added the clearing of
> isert_conn->cm_id to isert_connect_error(), it probably makes sense to
> use isert_conn->device->ib_device, and avoid dereferencing
> isert_conn->cm_id before connection is established.
> 
> Here's a quick (untested) patch to do this for recv/send done callbacks,
> and avoid using isert_conn->cm_id during isert_rdma_accept().
> 
> Sagi + Co, WDYT..?

Just tested this patch, I wasn't able to reproduce the NULL pointer
dereference or any other bugs, so this fix seems safe enough to me.

Tested-by: Andrea Righi <righi.andrea@gmail.com>

> 
> diff --git a/drivers/infiniband/ulp/isert/ib_isert.c b/drivers/infiniband/ulp/isert/ib_isert.c
> index fcbed35..f7f97f3 100644
> --- a/drivers/infiniband/ulp/isert/ib_isert.c
> +++ b/drivers/infiniband/ulp/isert/ib_isert.c
> @@ -52,7 +52,7 @@
>  static int
>  isert_login_post_recv(struct isert_conn *isert_conn);
>  static int
> -isert_rdma_accept(struct isert_conn *isert_conn);
> +isert_rdma_accept(struct isert_conn *isert_conn, struct rdma_cm_id *cm_id);
>  struct rdma_cm_id *isert_setup_id(struct isert_np *isert_np);
>  
>  static void isert_release_work(struct work_struct *work);
> @@ -543,7 +543,7 @@
>  	if (ret)
>  		goto out_conn_dev;
>  
> -	ret = isert_rdma_accept(isert_conn);
> +	ret = isert_rdma_accept(isert_conn, cma_id);
>  	if (ret)
>  		goto out_conn_dev;
>  
> @@ -1452,7 +1452,7 @@
>  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 = isert_conn->device->ib_device;
>  
>  	if (unlikely(wc->status != IB_WC_SUCCESS)) {
>  		isert_print_wc(wc, "login recv");
> @@ -1769,7 +1769,7 @@
>  isert_login_send_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 = isert_conn->device->ib_device;
>  	struct iser_tx_desc *tx_desc = cqe_to_tx_desc(wc->wr_cqe);
>  
>  	if (unlikely(wc->status != IB_WC_SUCCESS)) {
> @@ -2369,9 +2369,8 @@ struct rdma_cm_id *
>  }
>  
>  static int
> -isert_rdma_accept(struct isert_conn *isert_conn)
> +isert_rdma_accept(struct isert_conn *isert_conn, struct rdma_cm_id *cm_id)
>  {
> -	struct rdma_cm_id *cm_id = isert_conn->cm_id;
>  	struct rdma_conn_param cp;
>  	int ret;
>  	struct iser_cm_hdr rsp_hdr;

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

[Sagi Grimberg]

> Just tested this patch, I wasn't able to reproduce the NULL pointer
> dereference or any other bugs, so this fix seems safe enough to me.
> 
> Tested-by: Andrea Righi <righi.andrea@gmail.com>

Can you test just the one liner fix below?

>> @@ -1452,7 +1452,7 @@
>>   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 = isert_conn->device->ib_device;
>>   
>>   	if (unlikely(wc->status != IB_WC_SUCCESS)) {
>>   		isert_print_wc(wc, "login recv");

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

[Andrea Righi]

On Thu, Jun 29, 2017 at 08:36:51AM +0300, Sagi Grimberg wrote:
> 
> >Just tested this patch, I wasn't able to reproduce the NULL pointer
> >dereference or any other bugs, so this fix seems safe enough to me.
> >
> >Tested-by: Andrea Righi <righi.andrea@gmail.com>
> 
> Can you test just the one liner fix below?
> 
> >>@@ -1452,7 +1452,7 @@
> >>  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 = isert_conn->device->ib_device;
> >>  	if (unlikely(wc->status != IB_WC_SUCCESS)) {
> >>  		isert_print_wc(wc, "login recv");

I'll test also this one-liner fix as soon as I can.

But I can say that I'm pretty sure it will work as well, because all the
previous NULL pointer dereferences that we've got in the past happened
all 100% in isert_login_recv_done(). The other cases are probably a safe
precaution, but they can't really happen.

-Andrea

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

[Sagi Grimberg]

>> Can you test just the one liner fix below?
>>
>>>> @@ -1452,7 +1452,7 @@
>>>>   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 = isert_conn->device->ib_device;
>>>>   	if (unlikely(wc->status != IB_WC_SUCCESS)) {
>>>>   		isert_print_wc(wc, "login recv");
> 
> I'll test also this one-liner fix as soon as I can.
> 
> But I can say that I'm pretty sure it will work as well, because all the
> previous NULL pointer dereferences that we've got in the past happened
> all 100% in isert_login_recv_done(). The other cases are probably a safe
> precaution, but they can't really happen.

Agree, I'd prefer to start with a surgical fix before moving forward.

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

[Nicholas A. Bellinger]

On Thu, 2017-06-29 at 11:28 +0300, Sagi Grimberg wrote:
> >> Can you test just the one liner fix below?
> >>
> >>>> @@ -1452,7 +1452,7 @@
> >>>>   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 = isert_conn->device->ib_device;
> >>>>   	if (unlikely(wc->status != IB_WC_SUCCESS)) {
> >>>>   		isert_print_wc(wc, "login recv");
> > 
> > I'll test also this one-liner fix as soon as I can.
> > 
> > But I can say that I'm pretty sure it will work as well, because all the
> > previous NULL pointer dereferences that we've got in the past happened
> > all 100% in isert_login_recv_done(). The other cases are probably a safe
> > precaution, but they can't really happen.
> 
> Agree, I'd prefer to start with a surgical fix before moving forward.

Sounds fine.  The single line fix above in isert_login_recv_done() has
been queued up in target-pending/for-next with Andrea's Tested-by and
your Reviewed-by:

https://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending.git/commit/?h=for-next&id=702c0f17403765cc5aa1c18f6ea6eb549c1bac9b

Please let me know if there are any other issues wrt the surgical fix.

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]

[-- Attachment #1: Type: text/plain, Size: 3929 bytes --]

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@leblancnet.us> wrote:
> > > On Tue, Jun 20, 2017 at 12:54 PM, Robert LeBlanc <robert@leblancnet.us> 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@gmail.com>
> Signed-off-by: Robert LeBlanc <robert@leblancnet.us>
> ---
>  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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