[PATCH v2 1/3] xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling

[PATCH v2 1/3] xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling

[Simon Gaiser]

Commit fd8aa9095a95 ("xen: optimize xenbus driver for multiple
concurrent xenstore accesses") made a subtle change to the semantic of
xenbus_dev_request_and_reply() and xenbus_transaction_end().

Before on an error response to XS_TRANSACTION_END
xenbus_dev_request_and_reply() would not decrement the active
transaction counter. But xenbus_transaction_end() has always counted the
transaction as finished regardless of the response.

The new behavior is that xenbus_dev_request_and_reply() and
xenbus_transaction_end() will always count the transaction as finished
regardless the response code (handled in xs_request_exit()).

But xenbus_dev_frontend tries to end a transaction on closing of the
device if the XS_TRANSACTION_END failed before. Trying to close the
transaction twice corrupts the reference count. So fix this by also
considering a transaction closed if we have sent XS_TRANSACTION_END once
regardless of the return code.

Cc: <stable@vger.kernel.org> # 4.11
Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>
---
 drivers/xen/xenbus/xenbus_dev_frontend.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index a493e99bed21..81a84b3c1c50 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -365,7 +365,7 @@ void xenbus_dev_queue_reply(struct xb_req_data *req)
 			if (WARN_ON(rc))
 				goto out;
 		}
-	} else if (req->msg.type == XS_TRANSACTION_END) {
+	} else if (req->type == XS_TRANSACTION_END) {
 		trans = xenbus_get_transaction(u, req->msg.tx_id);
 		if (WARN_ON(!trans))
 			goto out;
-- 
2.16.2

[PATCH v2 2/3] xen: xenbus: Catch closing of non existent transactions

[Simon Gaiser]

Users of the xenbus functions should never close a non existent
transaction (for example by trying to closing the same transaction
twice) but better catch it in xs_request_exit() than to corrupt the
reference counter.

Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>
---
 drivers/xen/xenbus/xenbus_xs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index 3f3b29398ab8..49a3874ae6bb 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -140,7 +140,9 @@ void xs_request_exit(struct xb_req_data *req)
 	spin_lock(&xs_state_lock);
 	xs_state_users--;
 	if ((req->type == XS_TRANSACTION_START && req->msg.type == XS_ERROR) ||
-	    req->type == XS_TRANSACTION_END)
+	    (req->type == XS_TRANSACTION_END &&
+	     !WARN_ON_ONCE(req->msg.type == XS_ERROR &&
+			   !strcmp(req->body, "ENOENT"))))
 		xs_state_users--;
 	spin_unlock(&xs_state_lock);
 
-- 
2.16.2

Re: [PATCH v2 2/3] xen: xenbus: Catch closing of non existent transactions

[Juergen Gross]

On 15/03/18 03:43, Simon Gaiser wrote:
> Users of the xenbus functions should never close a non existent
> transaction (for example by trying to closing the same transaction
> twice) but better catch it in xs_request_exit() than to corrupt the
> reference counter.
> 
> Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

[PATCH v2 3/3] xen: xenbus_dev_frontend: Verify body of XS_TRANSACTION_END

[Simon Gaiser]

By guaranteeing that the argument of XS_TRANSACTION_END is valid we can
assume that the transaction has been closed when we get an XS_ERROR
response from xenstore (Note that we already verify that it's a valid
transaction id).

Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>
---
 drivers/xen/xenbus/xenbus_dev_frontend.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index 81a84b3c1c50..0d6d9264d6a9 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -429,6 +429,10 @@ static int xenbus_write_transaction(unsigned msg_type,
 {
 	int rc;
 	struct xenbus_transaction_holder *trans = NULL;
+	struct {
+		struct xsd_sockmsg hdr;
+		char body[];
+	} *msg = (void *)u->u.buffer;
 
 	if (msg_type == XS_TRANSACTION_START) {
 		trans = kzalloc(sizeof(*trans), GFP_KERNEL);
@@ -437,11 +441,15 @@ static int xenbus_write_transaction(unsigned msg_type,
 			goto out;
 		}
 		list_add(&trans->list, &u->transactions);
-	} else if (u->u.msg.tx_id != 0 &&
-		   !xenbus_get_transaction(u, u->u.msg.tx_id))
+	} else if (msg->hdr.tx_id != 0 &&
+		   !xenbus_get_transaction(u, msg->hdr.tx_id))
 		return xenbus_command_reply(u, XS_ERROR, "ENOENT");
+	else if (msg_type == XS_TRANSACTION_END &&
+		 !(msg->hdr.len == 2 &&
+		   (!strcmp(msg->body, "T") || !strcmp(msg->body, "F"))))
+		return xenbus_command_reply(u, XS_ERROR, "EINVAL");
 
-	rc = xenbus_dev_request_and_reply(&u->u.msg, u);
+	rc = xenbus_dev_request_and_reply(&msg->hdr, u);
 	if (rc && trans) {
 		list_del(&trans->list);
 		kfree(trans);
-- 
2.16.2

Re: [PATCH v2 3/3] xen: xenbus_dev_frontend: Verify body of XS_TRANSACTION_END

[Juergen Gross]

On 15/03/18 03:43, Simon Gaiser wrote:
> By guaranteeing that the argument of XS_TRANSACTION_END is valid we can
> assume that the transaction has been closed when we get an XS_ERROR
> response from xenstore (Note that we already verify that it's a valid
> transaction id).
> 
> Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

Re: [PATCH v2 1/3] xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling

[Juergen Gross]

On 15/03/18 03:43, Simon Gaiser wrote:
> Commit fd8aa9095a95 ("xen: optimize xenbus driver for multiple
> concurrent xenstore accesses") made a subtle change to the semantic of
> xenbus_dev_request_and_reply() and xenbus_transaction_end().
> 
> Before on an error response to XS_TRANSACTION_END
> xenbus_dev_request_and_reply() would not decrement the active
> transaction counter. But xenbus_transaction_end() has always counted the
> transaction as finished regardless of the response.
> 
> The new behavior is that xenbus_dev_request_and_reply() and
> xenbus_transaction_end() will always count the transaction as finished
> regardless the response code (handled in xs_request_exit()).
> 
> But xenbus_dev_frontend tries to end a transaction on closing of the
> device if the XS_TRANSACTION_END failed before. Trying to close the
> transaction twice corrupts the reference count. So fix this by also
> considering a transaction closed if we have sent XS_TRANSACTION_END once
> regardless of the return code.
> 
> Cc: <stable@vger.kernel.org> # 4.11
> Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
> Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

Re: [PATCH v2 1/3] xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling

[Boris Ostrovsky]

On 03/14/2018 10:43 PM, Simon Gaiser wrote:
> Commit fd8aa9095a95 ("xen: optimize xenbus driver for multiple
> concurrent xenstore accesses") made a subtle change to the semantic of
> xenbus_dev_request_and_reply() and xenbus_transaction_end().
>
> Before on an error response to XS_TRANSACTION_END
> xenbus_dev_request_and_reply() would not decrement the active
> transaction counter. But xenbus_transaction_end() has always counted the
> transaction as finished regardless of the response.
>
> The new behavior is that xenbus_dev_request_and_reply() and
> xenbus_transaction_end() will always count the transaction as finished
> regardless the response code (handled in xs_request_exit()).
>
> But xenbus_dev_frontend tries to end a transaction on closing of the
> device if the XS_TRANSACTION_END failed before. Trying to close the
> transaction twice corrupts the reference count. So fix this by also
> considering a transaction closed if we have sent XS_TRANSACTION_END once
> regardless of the return code.
>
> Cc: <stable@vger.kernel.org> # 4.11
> Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
> Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>

Applied the series to for-linus-4.17

-boris