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Date: Sat, 25 May 2019 20:15:01 +0800 From: Muchun Song <smuchun@...il.com> To: Greg KH <gregkh@...uxfoundation.org> Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Prateek Sood <prsood@...eaurora.org>, Mukesh Ojha <mojha@...eaurora.org>, gkohli@...eaurora.org, linux-kernel <linux-kernel@...r.kernel.org>, linux-arm-msm <linux-arm-msm@...r.kernel.org>, zhaowuyun@...gtech.com Subject: Re: [PATCH v4] driver core: Fix use-after-free and double free on glue directory Hi greg k-h, Greg KH <gregkh@...uxfoundation.org> 于2019年5月25日周六 上午3:04写道: > > On Thu, May 16, 2019 at 10:23:42PM +0800, Muchun Song wrote: > > There is a race condition between removing glue directory and adding a new > > device under the glue directory. It can be reproduced in following test: > > <snip> > > Is this related to: > Subject: [PATCH v3] drivers: core: Remove glue dirs early only when refcount is 1 > > ? > > If so, why is the solution so different? In the v1 patch, the solution is that remove glue dirs early only when refcount is 1. So the v1 patch like below: @@ -1825,7 +1825,7 @@ static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir) return; mutex_lock(&gdp_mutex); - if (!kobject_has_children(glue_dir)) + if (!kobject_has_children(glue_dir) && kref_read(&glue_dir->kref) == 1) kobject_del(glue_dir); kobject_put(glue_dir); mutex_unlock(&gdp_mutex); ----------------------------------------------------------------------- But from Ben's suggestion as below: I find relying on the object count for such decisions rather fragile as it could be taken temporarily for other reasons, couldn't it ? In which case we would just fail... Ideally, the looking up of the glue dir and creation of its child should be protected by the same lock instance (the gdp_mutex in that case). ----------------------------------------------------------------------- So another solution is used from Ben's suggestion in the v2 patch. But I forgot to update the commit message until the v4 patch. Thanks. Yours, Muchun
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