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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Eric Biggers <ebiggers3@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Kees Cook <keescook@chromium.org>,
	syzbot 
	<bot+e93a80c1bb7c5c56e522461c149f8bf55eab1b2b@syzkaller.appspotmail.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Subject: Re: [PATCH v2] fs: Allow opening only regular files during execve().
Date: Tue, 19 Feb 2019 18:51:49 +0900
Message-ID: <41c0632d-ba5e-35be-a44f-c918fe6fd8dd@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <201902120526.x1C5QYXX092667@www262.sakura.ne.jp>

Hello, Al.

What would you suggest if FMODE_EXEC is not the right choice?

On 2019/01/22 9:51, Kees Cook wrote:
> On Tue, Jan 22, 2019 at 10:18 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
>> We are *NOT* going to use current->in_execve to propagate that information.
>> Come up with a cleaner solution, if you care, but this one is a non-starter.
>> Too ugly to live.  Sorry.
> 
> What would you suggest for a cleaner indication of being in an execve?
> 

On 2019/02/12 14:26, Tetsuo Handa wrote:
> Tetsuo Handa wrote:
>> Andrew Morton wrote:
>>>> --- a/fs/open.c
>>>> +++ b/fs/open.c
>>>> @@ -733,6 +733,12 @@ static int do_dentry_open(struct file *f,
>>>>  		return 0;
>>>>  	}
>>>>  
>>>> +	/* Any file opened for execve()/uselib() has to be a regular file. */
>>>> +	if (unlikely(f->f_flags & FMODE_EXEC && !S_ISREG(inode->i_mode))) {
>>>> +		error = -EACCES;
>>>> +		goto cleanup_file;
>>>> +	}
>>>> +
>>>>  	if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
>>>>  		error = get_write_access(inode);
>>>>  		if (unlikely(error))
>>>
>>> This change sounds legitimate for various other reasons, but it's a
>>> concern that this locking error occurred in the first place.  There's a
>>> problem somewhere (probably the pipe code) which may bite us in other
>>> situations, even with this workaround in place.
>>>
>>>
>>
>> This error seems to be introduced in 2.6.39-rc1 by commit a9712bc12c40c172
>> ("deal with races in /proc/*/{syscall,stack,personality}"). Thus, I don't
>> think that this patch will bite us in other situations.
>> Al, how do you want to handle this?
>>
> 
> According to bisection, commit 8924feff66f35fe2 ("splice: lift pipe_lock out of splice_to_pipe()")
> added in 4.9-rc1 is the trigger of this deadlock. Thus, the fix needs to go to 4.9+.

  reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <001a113f711ae2110c055f45acb8@google.com>
2017-12-02  8:12 ` possible deadlock in seq_read syzbot
2017-12-03 22:02 ` syzbot
2017-12-12 22:06 ` Eric Biggers
2017-12-27 18:30   ` Dmitry Vyukov
2018-08-27 18:20   ` Kees Cook
2018-08-27 20:57     ` Dmitry Vyukov
2019-01-21 10:14       ` [PATCH] fs: Allow opening only regular files during execve() Tetsuo Handa
2019-01-21 20:24         ` Kees Cook
2019-01-21 21:18         ` Al Viro
2019-01-22  0:50           ` [PATCH v2] " Tetsuo Handa
2019-01-28 23:42             ` Andrew Morton
2019-02-12  2:01               ` Tetsuo Handa
2019-02-12  5:26               ` Tetsuo Handa
2019-02-19  9:51                 ` Tetsuo Handa [this message]
2019-01-22  0:51           ` [PATCH] " Kees Cook

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