linux-kernel - Re: [patch 2/9] unprivileged mounts: allow unprivileged umount

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20080114214841.GB6704@sergelap.austin.ibm.com>
Date:	Mon, 14 Jan 2008 15:48:41 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	akpm@...ux-foundation.org, hch@...radead.org, serue@...ibm.com,
	viro@....linux.org.uk, ebiederm@...ssion.com, kzak@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, util-linux-ng@...r.kernel.org
Subject: Re: [patch 2/9] unprivileged mounts: allow unprivileged umount

Quoting Miklos Szeredi (miklos@...redi.hu):
> From: Miklos Szeredi <mszeredi@...e.cz>
> 
> The owner doesn't need sysadmin capabilities to call umount().
> 
> Similar behavior as umount(8) on mounts having "user=UID" option in /etc/mtab.
> The difference is that umount also checks /etc/fstab, presumably to exclude
> another mount on the same mountpoint.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>

Acked-by: Serge Hallyn <serue@...ibm.com>

> ---
> 
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2008-01-03 20:52:38.000000000 +0100
> +++ linux/fs/namespace.c	2008-01-03 21:14:16.000000000 +0100
> @@ -894,6 +894,27 @@ static int do_umount(struct vfsmount *mn
>  	return retval;
>  }
> 
> +static bool is_mount_owner(struct vfsmount *mnt, uid_t uid)
> +{
> +	return (mnt->mnt_flags & MNT_USER) && mnt->mnt_uid == uid;
> +}
> +
> +/*
> + * umount is permitted for
> + *  - sysadmin
> + *  - mount owner, if not forced umount
> + */
> +static bool permit_umount(struct vfsmount *mnt, int flags)
> +{
> +	if (capable(CAP_SYS_ADMIN))
> +		return true;
> +
> +	if (flags & MNT_FORCE)
> +		return false;
> +
> +	return is_mount_owner(mnt, current->fsuid);
> +}
> +
>  /*
>   * Now umount can handle mount points as well as block devices.
>   * This is important for filesystems which use unnamed block devices.
> @@ -917,7 +938,7 @@ asmlinkage long sys_umount(char __user *
>  		goto dput_and_out;
> 
>  	retval = -EPERM;
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!permit_umount(nd.path.mnt, flags))
>  		goto dput_and_out;
> 
>  	retval = do_umount(nd.path.mnt, flags);
> 
> --
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/