linux-kernel - Re: [PATCH 06/20] signal/sh: Use force_sig(SIGKILL) instead of do_group

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Message-ID: <202110210907.F89199BB2@keescook>
Date:   Thu, 21 Oct 2021 09:08:53 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org
Subject: Re: [PATCH 06/20] signal/sh: Use force_sig(SIGKILL) instead of
 do_group_exit(SIGKILL)

On Wed, Oct 20, 2021 at 12:43:52PM -0500, Eric W. Biederman wrote:
> Today the sh code allocates memory the first time a process uses
> the fpu.  If that memory allocation fails, kill the affected task
> with force_sig(SIGKILL) rather than do_group_exit(SIGKILL).
> 
> Calling do_group_exit from an exception handler can potentially lead
> to dead locks as do_group_exit is not designed to be called from
> interrupt context.  Instead use force_sig(SIGKILL) to kill the
> userspace process.  Sending signals in general and force_sig in
> particular has been tested from interrupt context so there should be
> no problems.
> 
> Cc: Yoshinori Sato <ysato@...rs.sourceforge.jp>
> Cc: Rich Felker <dalias@...c.org>
> Cc: linux-sh@...r.kernel.org
> Fixes: 0ea820cf9bf5 ("sh: Move over to dynamically allocated FPU context.")
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Looks sane; there should be no observable changes.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook