linux-kernel - Re: [6.8-rc1 Regression] Unable to exec apparmor

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Message-ID: <f1ed6129-409a-484b-a7f4-71b2be90b60f@I-love.SAKURA.ne.jp>
Date: Sat, 27 Jan 2024 20:23:06 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kees Cook <keescook@...omium.org>, Paul Moore <paul@...l-moore.com>,
        Kevin Locke <kevin@...inlocke.name>,
        Josh Triplett <josh@...htriplett.org>,
        Mateusz Guzik <mjguzik@...il.com>, Al Viro <viro@...iv.linux.org.uk>,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org,
        Kentaro Takeda <takedakn@...data.co.jp>,
        John Johansen <john.johansen@...onical.com>
Subject: Re: [6.8-rc1 Regression] Unable to exec apparmor_parser from
 virt-aa-helper

On 2024/01/27 20:00, Tetsuo Handa wrote:
> On 2024/01/27 16:04, Tetsuo Handa wrote:
>> If we can accept revival of security_bprm_free(), we can "get rid of current->in_execve flag"
>> and "stop saving things across two *independent* execve() calls".
> 
> Oops, I found a bug in TOMOYO (and possibly in AppArmor as well).
> TOMOYO has to continue depending on current->in_execve flag even if
> security_bprm_free() is revived.

No. We can "get rid of current->in_execve flag" and "stop saving things across
two *independent* execve() calls".

> @@ -327,9 +322,13 @@ static int tomoyo_file_fcntl(struct file *file, unsigned int cmd,
>   */
>  static int tomoyo_file_open(struct file *f)
>  {
> -       /* Don't check read permission here if called from execve(). */
> -       /* Illogically, FMODE_EXEC is in f_flags, not f_mode. */
> -       if (f->f_flags & __FMODE_EXEC)
> +       /*
> +        * Don't check read permission here if called from execve() for
> +        * the first time of that execve() request, for execute permission
> +        * will be checked at tomoyo_bprm_check_security() with argv/envp
> +        * taken into account.
> +        */
> +       if (current->in_execve && !tomoyo_task(current)->old_domain_info)

Since "f->f_flags & __FMODE_EXEC" == "current->in_execve", TOMOYO can continue using
"f->f_flags & __FMODE_EXEC", provided that tomoyo_task(current)->old_domain_info is
reset to NULL via security_bprm_free() callback when previous execve() request failed.

That is, if security_bprm_free() is revived, we can also get rid of current->in_execve.