xen/blkback: prevent leak of mode during multiple backend_changed calls

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

Signed-off-by Olaf Hering <[email protected]>

---

!! Not compile tested !!

 drivers/block/xen-blkback/xenbus.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

drivers/block/xen-blkback/xenbus.c +7 -5

index a6585a4..8650b19 100644
@@ -502,7 +502,7 @@ static void backend_changed(struct xenbus_watch *watch,
 		= container_of(watch, struct backend_info, backend_watch);
 	struct xenbus_device *dev = be->dev;
 	int cdrom = 0;
-	char *device_type;
+	char *mode, *device_type;
 
 	DPRINTK("");
 

@@ -528,13 +528,15 @@ static void backend_changed(struct xenbus_watch *watch,
 		return;
 	}
 
-	be->mode = xenbus_read(XBT_NIL, dev->nodename, "mode", NULL);
-	if (IS_ERR(be->mode)) {
-		err = PTR_ERR(be->mode);
+	mode = xenbus_read(XBT_NIL, dev->nodename, "mode", NULL);
+	kfree(be->mode);
+	if (IS_ERR(mode)) {
+		err = PTR_ERR(mode);
 		be->mode = NULL;
 		xenbus_dev_fatal(dev, err, "reading mode");
 		return;
 	}
+	be->mode = mode;
 
 	device_type = xenbus_read(XBT_NIL, dev->otherend, "device-type", NULL);
 	if (!IS_ERR(device_type)) {

@@ -555,7 +557,7 @@ static void backend_changed(struct xenbus_watch *watch,
 		be->minor = minor;
 
 		err = xen_vbd_create(be->blkif, handle, major, minor,
-				 (NULL == strchr(be->mode, 'w')), cdrom);
+				 (NULL == strchr(mode, 'w')), cdrom);
 		if (err) {
 			be->major = 0;
 			be->minor = 0;

Signature · 1 line

1.8.0.1

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

Signed-off-by Olaf Hering <[email protected]>

---

!! Not compile tested !!

 drivers/block/xen-blkback/xenbus.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

drivers/block/xen-blkback/xenbus.c +7 -5

index a6585a4..8650b19 100644
@@ -502,7 +502,7 @@ static void backend_changed(struct xenbus_watch *watch,
 		= container_of(watch, struct backend_info, backend_watch);
 	struct xenbus_device *dev = be->dev;
 	int cdrom = 0;
-	char *device_type;
+	char *mode, *device_type;
 
 	DPRINTK("");
 

@@ -528,13 +528,15 @@ static void backend_changed(struct xenbus_watch *watch,
 		return;
 	}
 
-	be->mode = xenbus_read(XBT_NIL, dev->nodename, "mode", NULL);
-	if (IS_ERR(be->mode)) {
-		err = PTR_ERR(be->mode);
+	mode = xenbus_read(XBT_NIL, dev->nodename, "mode", NULL);
+	kfree(be->mode);
+	if (IS_ERR(mode)) {
+		err = PTR_ERR(mode);
 		be->mode = NULL;
 		xenbus_dev_fatal(dev, err, "reading mode");
 		return;
 	}
+	be->mode = mode;
 
 	device_type = xenbus_read(XBT_NIL, dev->otherend, "device-type", NULL);
 	if (!IS_ERR(device_type)) {

@@ -555,7 +557,7 @@ static void backend_changed(struct xenbus_watch *watch,
 		be->minor = minor;
 
 		err = xen_vbd_create(be->blkif, handle, major, minor,
-				 (NULL == strchr(be->mode, 'w')), cdrom);
+				 (NULL == strchr(mode, 'w')), cdrom);
 		if (err) {
 			be->major = 0;
 			be->minor = 0;

Signature · 1 line

1.8.0.1

Quoted 3 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

As said before - this is one possible route to take. But did you consider at all the alternative of preventing the function from getting called more than once for a given device? As also said before, I think that would have other bad effects, and hence should be preferred (and would likely also result in a smaller patch).

Quoted 3 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

As said before - this is one possible route to take. But did you consider at all the alternative of preventing the function from getting called more than once for a given device? As also said before, I think that would have other bad effects, and hence should be preferred (and would likely also result in a smaller patch).

Quoted 1 line

Quoted 1 line · Olaf Hering

Quoted 10 lines · Jan Beulich

Quoted 3 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

As said before - this is one possible route to take. But did you consider at all the alternative of preventing the function from getting called more than once for a given device? As also said before, I think that would have other bad effects, and hence should be preferred (and would likely also result in a smaller patch).

Maybe it could be done like this, adding a flag to the backend device and exit early if its called twice.

drivers/block/xen-blkback/xenbus.c +13 -1

@@ -28,6 +28,7 @@ struct backend_info {
 	unsigned		major;
 	unsigned		minor;
 	char			*mode;
+	unsigned		alive;
 };
 
 static struct kmem_cache *xen_blkif_cachep;

@@ -506,6 +507,9 @@ static void backend_changed(struct xenbus_watch *watch,
 
 	DPRINTK("");
 
+	if (be->alive)
+		return;
+
 	err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x",
 			   &major, &minor);
 	if (XENBUS_EXIST_ERR(err)) {

@@ -548,8 +552,11 @@ static void backend_changed(struct xenbus_watch *watch,
 		char *p = strrchr(dev->otherend, '/') + 1;
 		long handle;
 		err = strict_strtoul(p, 0, &handle);
-		if (err)
+		if (err) {
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
+		}
 
 		be->major = major;
 		be->minor = minor;

@@ -560,6 +567,8 @@ static void backend_changed(struct xenbus_watch *watch,
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating vbd structure");
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
 		}
 

@@ -569,10 +578,13 @@ static void backend_changed(struct xenbus_watch 
 *watch,
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating sysfs entries");
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
 		}
 
 		/* We're potentially connected now */
+		be->alive = 1;
 		xen_update_blkif_status(be->blkif);
 	}

}

Signature · 1 line

1.8.0.1

Quoted 1 line

Quoted 1 line · Olaf Hering

Quoted 10 lines · Jan Beulich

Quoted 3 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

As said before - this is one possible route to take. But did you consider at all the alternative of preventing the function from getting called more than once for a given device? As also said before, I think that would have other bad effects, and hence should be preferred (and would likely also result in a smaller patch).

Maybe it could be done like this, adding a flag to the backend device and exit early if its called twice.

drivers/block/xen-blkback/xenbus.c +13 -1

@@ -28,6 +28,7 @@ struct backend_info {
 	unsigned		major;
 	unsigned		minor;
 	char			*mode;
+	unsigned		alive;
 };
 
 static struct kmem_cache *xen_blkif_cachep;

@@ -506,6 +507,9 @@ static void backend_changed(struct xenbus_watch *watch,
 
 	DPRINTK("");
 
+	if (be->alive)
+		return;
+
 	err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x",
 			   &major, &minor);
 	if (XENBUS_EXIST_ERR(err)) {

@@ -548,8 +552,11 @@ static void backend_changed(struct xenbus_watch *watch,
 		char *p = strrchr(dev->otherend, '/') + 1;
 		long handle;
 		err = strict_strtoul(p, 0, &handle);
-		if (err)
+		if (err) {
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
+		}
 
 		be->major = major;
 		be->minor = minor;

@@ -560,6 +567,8 @@ static void backend_changed(struct xenbus_watch *watch,
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating vbd structure");
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
 		}
 

@@ -569,10 +578,13 @@ static void backend_changed(struct xenbus_watch 
 *watch,
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating sysfs entries");
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
 		}
 
 		/* We're potentially connected now */
+		be->alive = 1;
 		xen_update_blkif_status(be->blkif);
 	}

}

Signature · 1 line

1.8.0.1

Quoted 14 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

Quoted 10 lines · Jan Beulich

Quoted 3 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

As said before - this is one possible route to take. But did you consider at all the alternative of preventing the function from getting called more than once for a given device? As also said before, I think that would have other bad effects, and hence should be preferred (and would likely also result in a smaller patch).

Quoted 2 lines

Maybe it could be done like this, adding a flag to the backend device and exit early if its called twice.

Maybe, but it looks odd to me. But then again I had hoped Konrad would have an opinion here...

Quoted 14 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

Quoted 10 lines · Jan Beulich

Quoted 3 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

As said before - this is one possible route to take. But did you consider at all the alternative of preventing the function from getting called more than once for a given device? As also said before, I think that would have other bad effects, and hence should be preferred (and would likely also result in a smaller patch).

Quoted 2 lines

Maybe it could be done like this, adding a flag to the backend device and exit early if its called twice.

Maybe, but it looks odd to me. But then again I had hoped Konrad would have an opinion here...

Quoted 14 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

Quoted 10 lines · Jan Beulich

Quoted 3 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

As said before - this is one possible route to take. But did you consider at all the alternative of preventing the function from getting called more than once for a given device? As also said before, I think that would have other bad effects, and hence should be preferred (and would likely also result in a smaller patch).

Quoted 2 lines

Maybe it could be done like this, adding a flag to the backend device and exit early if its called twice.

Maybe, but it looks odd to me. But then again I had hoped Konrad would have an opinion here...

Also I don't see why you need to free be->mode now on all error paths - afaict it would still get freed when "be" gets freed (with your earlier patch).

Jan

Quoted 59 lines

drivers/block/xen-blkback/xenbus.c +13 -1

@@ -28,6 +28,7 @@ struct backend_info {
 	unsigned		major;
 	unsigned		minor;
 	char			*mode;
+	unsigned		alive;
 };
 
 static struct kmem_cache *xen_blkif_cachep;

@@ -506,6 +507,9 @@ static void backend_changed(struct xenbus_watch *watch,
 
 	DPRINTK("");
 
+	if (be->alive)
+		return;
+
 	err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x",
 			   &major, &minor);
 	if (XENBUS_EXIST_ERR(err)) {

@@ -548,8 +552,11 @@ static void backend_changed(struct xenbus_watch *watch,
 		char *p = strrchr(dev->otherend, '/') + 1;
 		long handle;
 		err = strict_strtoul(p, 0, &handle);
-		if (err)
+		if (err) {
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
+		}
 
 		be->major = major;
 		be->minor = minor;

@@ -560,6 +567,8 @@ static void backend_changed(struct xenbus_watch *watch,
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating vbd structure");
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
 		}
 

@@ -569,10 +578,13 @@ static void backend_changed(struct xenbus_watch 
 *watch,
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating sysfs entries");
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
 		}
 
 		/* We're potentially connected now */
+		be->alive = 1;
 		xen_update_blkif_status(be->blkif);
 	}

}

Signature · 1 line

1.8.0.1

Quoted 14 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

Quoted 10 lines · Jan Beulich

Quoted 3 lines

Quoted 1 line

Quoted 1 line · Olaf Hering

backend_changed might be called multiple times, which will leak be->mode. free the previous value before storing the current mode value.

As said before - this is one possible route to take. But did you consider at all the alternative of preventing the function from getting called more than once for a given device? As also said before, I think that would have other bad effects, and hence should be preferred (and would likely also result in a smaller patch).

Quoted 2 lines

Maybe it could be done like this, adding a flag to the backend device and exit early if its called twice.

Maybe, but it looks odd to me. But then again I had hoped Konrad would have an opinion here...

Also I don't see why you need to free be->mode now on all error paths - afaict it would still get freed when "be" gets freed (with your earlier patch).

Jan

Quoted 59 lines

drivers/block/xen-blkback/xenbus.c +13 -1

@@ -28,6 +28,7 @@ struct backend_info {
 	unsigned		major;
 	unsigned		minor;
 	char			*mode;
+	unsigned		alive;
 };
 
 static struct kmem_cache *xen_blkif_cachep;

@@ -506,6 +507,9 @@ static void backend_changed(struct xenbus_watch *watch,
 
 	DPRINTK("");
 
+	if (be->alive)
+		return;
+
 	err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x",
 			   &major, &minor);
 	if (XENBUS_EXIST_ERR(err)) {

@@ -548,8 +552,11 @@ static void backend_changed(struct xenbus_watch *watch,
 		char *p = strrchr(dev->otherend, '/') + 1;
 		long handle;
 		err = strict_strtoul(p, 0, &handle);
-		if (err)
+		if (err) {
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
+		}
 
 		be->major = major;
 		be->minor = minor;

@@ -560,6 +567,8 @@ static void backend_changed(struct xenbus_watch *watch,
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating vbd structure");
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
 		}
 

@@ -569,10 +578,13 @@ static void backend_changed(struct xenbus_watch 
 *watch,
 			be->major = 0;
 			be->minor = 0;
 			xenbus_dev_fatal(dev, err, "creating sysfs entries");
+			kfree(be->mode);
+			be->mode = NULL;
 			return;
 		}
 
 		/* We're potentially connected now */
+		be->alive = 1;
 		xen_update_blkif_status(be->blkif);
 	}

}

Signature · 1 line

1.8.0.1