mnt: Refactor the logic for mounting sysfs and proc in a user namespace
Fresh mounts of proc and sysfs are a very special case that works very
much like a bind mount. Unfortunately the current structure can not
preserve the MNT_LOCK... mount flags. Therefore refactor the logic
into a form that can be modified to preserve those lock bits.
Add a new filesystem flag FS_USERNS_VISIBLE that requires some mount
of the filesystem be fully visible in the current mount namespace,
before the filesystem may be mounted.
Move the logic for calling fs_fully_visible from proc and sysfs into
fs/namespace.c where it has greater access to mount namespace state.
Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/fs/namespace.c b/fs/namespace.c
index 1b9e111..8e7edaf 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2332,6 +2332,8 @@
return err;
}
+static bool fs_fully_visible(struct file_system_type *fs_type);
+
/*
* create a new mount for userspace and request it to be added into the
* namespace's tree
@@ -2363,6 +2365,10 @@
flags |= MS_NODEV;
mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
}
+ if (type->fs_flags & FS_USERNS_VISIBLE) {
+ if (!fs_fully_visible(type))
+ return -EPERM;
+ }
}
mnt = vfs_kern_mount(type, flags, name, data);
@@ -3164,7 +3170,7 @@
return chrooted;
}
-bool fs_fully_visible(struct file_system_type *type)
+static bool fs_fully_visible(struct file_system_type *type)
{
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
struct mount *mnt;
diff --git a/fs/proc/root.c b/fs/proc/root.c
index b7fa4bf..64e1ab6 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -112,9 +112,6 @@
ns = task_active_pid_ns(current);
options = data;
- if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
- return ERR_PTR(-EPERM);
-
/* Does the mounter have privilege over the pid namespace? */
if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
return ERR_PTR(-EPERM);
@@ -159,7 +156,7 @@
.name = "proc",
.mount = proc_mount,
.kill_sb = proc_kill_sb,
- .fs_flags = FS_USERNS_MOUNT,
+ .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
};
void __init proc_root_init(void)
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 8a49486..1c6ac6f 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -31,9 +31,6 @@
bool new_sb;
if (!(flags & MS_KERNMOUNT)) {
- if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
- return ERR_PTR(-EPERM);
-
if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
return ERR_PTR(-EPERM);
}
@@ -58,7 +55,7 @@
.name = "sysfs",
.mount = sysfs_mount,
.kill_sb = sysfs_kill_sb,
- .fs_flags = FS_USERNS_MOUNT,
+ .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
};
int __init sysfs_init(void)