linux-kernel - Re: [PATCH] kernel/exit.c: pointer sighand could be uninitialized

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Message-ID: <20180503050650.GX30522@ZenIV.linux.org.uk>
Date:   Thu, 3 May 2018 06:06:50 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Yizhuo Zhai <yzhai003@....edu>
Cc:     mingo@...nel.org, keescook@...omium.org, akpm@...ux-foundation.org,
        paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        Chengyu Song <csong@...ucr.edu>,
        Zhiyun Qian <zhiyunq@...ucr.edu>
Subject: Re: [PATCH] kernel/exit.c: pointer sighand could be uninitialized

On Wed, May 02, 2018 at 06:48:57PM -0700, Yizhuo Zhai wrote:
> Variable 'sighand' could be uninitialized if probe_kernel_address fails
> (-EFAULT). The later use in the if statement may lead to undefined behavior.

Excuse me, but that's nonsense.  The value *copied* into it (in case
probe_kernel_address() has not failed) may be just as uninitialized.
If mere "compare uninitialized pointer value to NULL" can cause nasal demons to fly,
	* we are screwed anyway
	* the piece of crap compiler should be printed on sandpaper and used to
polish its authors.

Read the comments in there, please.  Especially the one regarding the second case.