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From: Christoph Hellwig <hch@lst.de>
To: sishuaigong <sishuai@purdue.edu>
Cc: jlbec@evilplan.org, hch@lst.de, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] configfs: fix a race in configfs_lookup()
Date: Mon, 23 Aug 2021 09:46:36 +0200	[thread overview]
Message-ID: <20210823074636.GA23822@lst.de> (raw)
In-Reply-To: <20210820214458.14087-1-sishuai@purdue.edu>

On Fri, Aug 20, 2021 at 05:44:58PM -0400, sishuaigong wrote:
> When configfs_lookup() is executing list_for_each_entry(),
> it is possible that configfs_dir_lseek() is calling list_del().
> Some unfortunate interleavings of them can cause a kernel NULL
> pointer dereference error
> 
> Thread 1                  Thread 2
> //configfs_dir_lseek()    //configfs_lookup()
> list_del(&cursor->s_sibling);
>                           list_for_each_entry(sd, ...)
> 
> Fix this bug by using list_for_each_entry_safe() instead.

I don't see how list_for_each_entry_safe would save you there.
You need a lock to sychronize the two, list_for_each_entry_safe
only ensures the next entry is looked up before iterating over
the current one.

  reply	other threads:[~2021-08-23  7:46 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-20 21:44 [PATCH] configfs: fix a race in configfs_lookup() sishuaigong
2021-08-23  7:46 ` Christoph Hellwig [this message]
     [not found]   ` <AFABA8B1-0523-4F8C-A9DD-DDC5638DEAF7@purdue.edu>
2021-08-23 17:08     ` Christoph Hellwig
2021-08-23 19:07       ` Gong, Sishuai
2021-08-25  5:19       ` Al Viro
2021-08-25  5:29         ` Christoph Hellwig
     [not found] <20210820213243.786-1-sishuai@purdue.edu>
2021-12-29  2:23 ` Gong, Sishuai

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