From: Al Viro <viro@zeniv.linux.org.uk>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] vfs: allow unprivileged whiteout creation
Date: Fri, 1 May 2020 05:14:44 +0100 [thread overview]
Message-ID: <20200501041444.GJ23230@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200409212859.GH28467@miu.piliscsaba.redhat.com>
On Thu, Apr 09, 2020 at 11:28:59PM +0200, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@redhat.com>
>
> Whiteouts, unlike real device node should not require privileges to create.
>
> The general concern with device nodes is that opening them can have side
> effects. The kernel already avoids zero major (see
> Documentation/admin-guide/devices.txt). To be on the safe side the patch
> explicitly forbids registering a char device with 0/0 number (see
> cdev_add()).
>
> This guarantees that a non-O_PATH open on a whiteout will fail with ENODEV;
> i.e. it won't have any side effect.
> int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
> {
> + bool is_whiteout = S_ISCHR(mode) && dev == WHITEOUT_DEV;
> int error = may_create(dir, dentry);
>
> if (error)
> return error;
>
> - if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD))
> + if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD) &&
> + !is_whiteout)
> return -EPERM;
Hmm... That exposes vfs_whiteout() to LSM; are you sure that you won't
end up with regressions for overlayfs on sufficiently weird setups?
next prev parent reply other threads:[~2020-05-01 4:14 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-09 21:28 [PATCH] vfs: allow unprivileged whiteout creation Miklos Szeredi
2020-05-01 4:14 ` Al Viro [this message]
2020-05-01 7:31 ` Miklos Szeredi
2020-05-01 14:46 ` Ondrej Mosnacek
2020-05-05 10:50 ` Miklos Szeredi
2020-05-01 18:39 ` Stephen Smalley
2020-05-04 11:18 ` Miklos Szeredi
2020-05-04 15:38 ` Stephen Smalley
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