Messages in this thread Patch in this message | | | Date | Thu, 6 Dec 2012 17:23:04 +0100 | From | Olaf Hering <> | Subject | Re: [PATCH] xen/blkback: prevent leak of mode during multiple backend_changed calls |
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On Wed, Dec 05, Jan Beulich wrote:
> >>> On 05.12.12 at 11:01, Olaf Hering <olaf@aepfle.de> wrote: > > 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.
Olaf
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index a6585a4..2822e73 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -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); } } -- 1.8.0.1
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