From: Al Viro <viro@ZenIV.linux.org.uk>
To: Joel Fernandes <joelaf@google.com>
Cc: linux-kernel@vger.kernel.org, Todd Kjos <tkjos@google.com>,
Arve Hjonnevag <arve@android.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] ashmem: Fix lockdep issue during llseek
Date: Fri, 26 Jan 2018 03:13:46 +0000 [thread overview]
Message-ID: <20180126031346.GW13338@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20180126024649.200330-1-joelaf@google.com>
On Thu, Jan 25, 2018 at 06:46:49PM -0800, Joel Fernandes wrote:
> ashmem_mutex create a chain of dependencies like so:
>
> (1)
> mmap syscall ->
> mmap_sem -> (acquired)
> ashmem_mmap
> ashmem_mutex (try to acquire)
> (block)
>
> (2)
> llseek syscall ->
> ashmem_llseek ->
> ashmem_mutex -> (acquired)
> inode_lock ->
> inode->i_rwsem (try to acquire)
> (block)
>
> (3)
> getdents ->
> iterate_dir ->
> inode_lock ->
> inode->i_rwsem (acquired)
> copy_to_user ->
> mmap_sem (try to acquire)
>
> There is a lock ordering created between mmap_sem and inode->i_rwsem
> during a syzcaller test, this patch fixes the issue by releasing the
> ashmem_mutex before the call to vfs_llseek, and reacquiring it after.
That looks odd. If this approach works, what the hell do you need
ashmem_mutex for in ashmem_llseek() in the first place? What is
it protecting there?
next prev parent reply other threads:[~2018-01-26 3:13 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-26 2:46 [PATCH] staging: ashmem: Fix lockdep issue during llseek Joel Fernandes
2018-01-26 3:13 ` Al Viro [this message]
2018-01-26 19:23 ` [PATCH] " Joel Fernandes
2018-01-26 19:25 ` Joel Fernandes
2018-01-26 19:39 ` Al Viro
2018-01-26 20:45 ` Joel Fernandes
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