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From: Kees Cook <keescook@chromium.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: Eric Biggers <ebiggers3@gmail.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Dmitry Vyukov <dvyukov@google.com>,
	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] fs: Allow opening only regular files during execve().
Date: Tue, 22 Jan 2019 09:24:07 +1300
Message-ID: <CAGXu5jL0JhcDt4u32c-60hYY_k-8u=42NHyz9bt3wNuTkmjOfQ@mail.gmail.com> (raw)
In-Reply-To: <d1e2488f-a969-30d4-5023-6fa85a4e3833@I-love.SAKURA.ne.jp>

On Mon, Jan 21, 2019 at 11:15 PM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> On Tue, Dec 12, 2017 at 2:06 PM, Eric Biggers <ebiggers3@gmail.com> wrote:
> > I'm not sure what the fix will be.  Maybe the proc handlers should take a
> > different lock instead of cred_guard_mutex.  Or perhaps execve should check that
> > the file is a regular file before it attempts to open it.
>
> We can easily distinguish open() from execve() and open() from others. ;-)
>
> From a8c559566f743eeec31c3cf5bab7a90b1ff7f78b Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Mon, 21 Jan 2019 13:55:11 +0900
> Subject: [PATCH] fs: Allow opening only regular files during execve().
>
> syzbot is hitting lockdep warning [1] due to trying to open a fifo during
> an execve() operation. But we don't need to open non regular files during
> an execve() operation, for all files which we will need are the executable
> file itself, the interpreter program, and libraries like ld-linux.so.2
> required by the executable file or the interpreter program.
>
> Since the manpage for execve(2) says that execve() returns EACCES when
> the file or a script interpreter is not a regular file, and we set
> current->in_execve flag during an execve() operation, let's bail out
> when current thread tried to open a non regular file during an execve()
> operation.
>
> [1] https://syzkaller.appspot.com/bug?id=b5095bfec44ec84213bac54742a82483aad578ce
>
> Reported-by: syzbot <syzbot+e93a80c1bb7c5c56e522461c149f8bf55eab1b2b@syzkaller.appspotmail.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

I like it!

Acked-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  fs/open.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/fs/open.c b/fs/open.c
> index 0285ce7dbd51..b2e7b04ade46 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -733,6 +733,12 @@ static int do_dentry_open(struct file *f,
>                 return 0;
>         }
>
> +       /* The file or a script interpreter has to be a regular file. */
> +       if (unlikely(current->in_execve && !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))
> --
> 2.17.1



-- 
Kees Cook

  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 [this message]
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
2019-01-22  0:51           ` [PATCH] " Kees Cook

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