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SubjectRe: [PATCH 05/11] fs: Allow superblock owner to access do_remount_sb()
On Fri, Dec 22, 2017 at 03:32:29PM +0100, Dongsu Park wrote:
> From: Seth Forshee <seth.forshee@canonical.com>
>
> Superblock level remounts are currently restricted to global
> CAP_SYS_ADMIN, as is the path for changing the root mount to
> read only on umount. Loosen both of these permission checks to
> also allow CAP_SYS_ADMIN in any namespace which is privileged
> towards the userns which originally mounted the filesystem.
>
> Patch v4 is available: https://patchwork.kernel.org/patch/8944631/
>
> Cc: linux-fsdevel@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Serge Hallyn <serge@hallyn.com>

Acked-by: Serge Hallyn <serge@hallyn.com>

> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> Signed-off-by: Dongsu Park <dongsu@kinvolk.io>
> ---
> fs/namespace.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/namespace.c b/fs/namespace.c
> index e158ec6b..830040d7 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -1589,7 +1589,7 @@ static int do_umount(struct mount *mnt, int flags)
> * Special case for "unmounting" root ...
> * we just try to remount it readonly.
> */
> - if (!capable(CAP_SYS_ADMIN))
> + if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
> return -EPERM;
> down_write(&sb->s_umount);
> if (!sb_rdonly(sb))
> @@ -2327,7 +2327,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
> down_write(&sb->s_umount);
> if (ms_flags & MS_BIND)
> err = change_mount_flags(path->mnt, ms_flags);
> - else if (!capable(CAP_SYS_ADMIN))
> + else if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
> err = -EPERM;
> else
> err = do_remount_sb(sb, sb_flags, data, 0);
> --
> 2.13.6

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