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From: Amir Goldstein <amir73il@gmail.com>
To: Miklos Szeredi <mszeredi@redhat.com>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH v2 04/10] ovl: make ioctl() safe
Date: Tue, 8 Dec 2020 13:11:19 +0200	[thread overview]
Message-ID: <CAOQ4uxhv+33nVxNQmZtf-uzZN0gMXBaDoiJYm88cWwa1fRQTTg@mail.gmail.com> (raw)
In-Reply-To: <20201207163255.564116-5-mszeredi@redhat.com>

On Mon, Dec 7, 2020 at 6:36 PM Miklos Szeredi <mszeredi@redhat.com> wrote:
>
> ovl_ioctl_set_flags() does a capability check using flags, but then the
> real ioctl double-fetches flags and uses potentially different value.
>
> The "Check the capability before cred override" comment misleading: user
> can skip this check by presenting benign flags first and then overwriting
> them to non-benign flags.
>
> Just remove the cred override for now, hoping this doesn't cause a
> regression.
>
> The proper solution is to create a new setxflags i_op (patches are in the
> works).
>
> Xfstests don't show a regression.
>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Looks reasonable

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

> ---
>  fs/overlayfs/file.c | 75 ++-------------------------------------------
>  1 file changed, 3 insertions(+), 72 deletions(-)
>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index efccb7c1f9bc..3cd1590f2030 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -541,46 +541,26 @@ static long ovl_real_ioctl(struct file *file, unsigned int cmd,
>                            unsigned long arg)
>  {
>         struct fd real;
> -       const struct cred *old_cred;
>         long ret;
>
>         ret = ovl_real_fdget(file, &real);
>         if (ret)
>                 return ret;
>
> -       old_cred = ovl_override_creds(file_inode(file)->i_sb);
>         ret = security_file_ioctl(real.file, cmd, arg);
>         if (!ret)
>                 ret = vfs_ioctl(real.file, cmd, arg);
> -       revert_creds(old_cred);
>
>         fdput(real);
>
>         return ret;
>  }
>


I wonder if we shouldn't leave a comment behind to explain
that no override is intentional.

I also wonder if "Permission model" sections shouldn't be saying
something about ioctl() (current task checks only)? or we just treat
this is a breakage of the permission model that needs to be fixed?

Thanks,
Amir.

  reply	other threads:[~2020-12-08 11:12 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-07 16:32 [PATCH v2 00/10] allow unprivileged overlay mounts Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 01/10] vfs: move cap_convert_nscap() call into vfs_setxattr() Miklos Szeredi
2020-12-09  1:53   ` James Morris
2021-01-01 17:35   ` Eric W. Biederman
2021-01-11 13:49     ` Miklos Szeredi
2021-01-12  0:14       ` Eric W. Biederman
2021-01-12  9:43         ` Miklos Szeredi
2021-01-12 10:04           ` Miklos Szeredi
2021-01-12 18:36           ` Eric W. Biederman
2021-01-12 18:49             ` Eric W. Biederman
2020-12-07 16:32 ` [PATCH v2 02/10] vfs: verify source area in vfs_dedupe_file_range_one() Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 03/10] ovl: check privs before decoding file handle Miklos Szeredi
2020-12-08 13:49   ` Amir Goldstein
2020-12-09 10:13     ` Miklos Szeredi
2020-12-09 16:20       ` Miklos Szeredi
2020-12-09 18:16         ` Amir Goldstein
2020-12-07 16:32 ` [PATCH v2 04/10] ovl: make ioctl() safe Miklos Szeredi
2020-12-08 11:11   ` Amir Goldstein [this message]
2020-12-10 15:18     ` Miklos Szeredi
2020-12-14  5:44       ` Amir Goldstein
2020-12-14 13:23         ` Miklos Szeredi
2020-12-14 14:47           ` Amir Goldstein
2020-12-09  1:57   ` James Morris
2020-12-10 15:19     ` Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 05/10] ovl: simplify file splice Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 06/10] ovl: user xattr Miklos Szeredi
2020-12-08 13:10   ` Amir Goldstein
2020-12-11 14:55     ` Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 07/10] ovl: do not fail when setting origin xattr Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 08/10] ovl: do not fail because of O_NOATIME Miklos Szeredi
2020-12-08 11:29   ` Amir Goldstein
2020-12-11 14:44     ` Miklos Szeredi
2020-12-14  5:49       ` Amir Goldstein
2020-12-07 16:32 ` [PATCH v2 09/10] ovl: do not get metacopy for userxattr Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 10/10] ovl: unprivieged mounts Miklos Szeredi
2020-12-08 10:27 ` [PATCH v2 00/10] allow unprivileged overlay mounts Tetsuo Handa
2020-12-10  8:56   ` John Johansen
2020-12-10  9:39     ` Miklos Szeredi
2020-12-15 11:03       ` John Johansen

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