[05/11] fs: Allow superblock owner to access do_remount_sb()

Submitted by Dongsu Park on Dec. 22, 2017, 2:32 p.m.

Details

Message ID 8dd484dceb9e96e5b67f21b8a0cf333753985e89.1512041070.git.dongsu@kinvolk.io
State New
Series "FUSE mounts from non-init user namespaces"
Headers show

Commit Message

Dongsu Park Dec. 22, 2017, 2:32 p.m.
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>
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(-)

Patch hide | download patch | download mbox

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);

Comments

Serge E. Hallyn Dec. 23, 2017, 3:30 a.m.
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