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SubjectRe: [REVIEW][PATCH 2/2] sysfs: Restrict mounting sysfs
On 27/08/13 22:46, Eric W. Biederman wrote:
>
> Don't allow mounting sysfs unless the caller has CAP_SYS_ADMIN rights
> over the net namespace. The principle here is if you create or have
> capabilities over it you can mount it, otherwise you get to live with
> what other people have mounted.
>
> Instead of testing this with a straight forward ns_capable call,
> perform this check the long and torturous way with kobject helpers,
> this keeps direct knowledge of namespaces out of sysfs, and preserves
> the existing sysfs abstractions.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

Hi,

Unfortunately this patch causes problems for me in v3.12-rc1 if
CONFIG_NET=n. Sysfs fails to mount with EPERM. Having networking enabled
seems an odd prerequisite for mounting sysfs :-P.

Cheers
James

> ---
> fs/sysfs/mount.c | 12 +++++++++---
> include/linux/kobject_ns.h | 2 ++
> lib/kobject.c | 12 ++++++++++++
> net/core/net-sysfs.c | 8 ++++++++
> 4 files changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
> index 4a2da3a..8c69ef4 100644
> --- a/fs/sysfs/mount.c
> +++ b/fs/sysfs/mount.c
> @@ -112,9 +112,15 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
> struct super_block *sb;
> int error;
>
> - if (!(flags & MS_KERNMOUNT) && !capable(CAP_SYS_ADMIN) &&
> - !fs_fully_visible(fs_type))
> - return ERR_PTR(-EPERM);
> + if (!(flags & MS_KERNMOUNT)) {
> + if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
> + return ERR_PTR(-EPERM);
> +
> + for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++) {
> + if (!kobj_ns_current_may_mount(type))
> + return ERR_PTR(-EPERM);
> + }
> + }
>
> info = kzalloc(sizeof(*info), GFP_KERNEL);
> if (!info)
> diff --git a/include/linux/kobject_ns.h b/include/linux/kobject_ns.h
> index f66b065..df32d25 100644
> --- a/include/linux/kobject_ns.h
> +++ b/include/linux/kobject_ns.h
> @@ -39,6 +39,7 @@ enum kobj_ns_type {
> */
> struct kobj_ns_type_operations {
> enum kobj_ns_type type;
> + bool (*current_may_mount)(void);
> void *(*grab_current_ns)(void);
> const void *(*netlink_ns)(struct sock *sk);
> const void *(*initial_ns)(void);
> @@ -50,6 +51,7 @@ int kobj_ns_type_registered(enum kobj_ns_type type);
> const struct kobj_ns_type_operations *kobj_child_ns_ops(struct kobject *parent);
> const struct kobj_ns_type_operations *kobj_ns_ops(struct kobject *kobj);
>
> +bool kobj_ns_current_may_mount(enum kobj_ns_type type);
> void *kobj_ns_grab_current(enum kobj_ns_type type);
> const void *kobj_ns_netlink(enum kobj_ns_type type, struct sock *sk);
> const void *kobj_ns_initial(enum kobj_ns_type type);
> diff --git a/lib/kobject.c b/lib/kobject.c
> index 4a1f33d..1853bd9 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -915,6 +915,18 @@ const struct kobj_ns_type_operations *kobj_ns_ops(struct kobject *kobj)
> return kobj_child_ns_ops(kobj->parent);
> }
>
> +bool kobj_ns_current_may_mount(enum kobj_ns_type type)
> +{
> + bool may_mount = false;
> +
> + spin_lock(&kobj_ns_type_lock);
> + if ((type > KOBJ_NS_TYPE_NONE) && (type < KOBJ_NS_TYPES) &&
> + kobj_ns_ops_tbl[type])
> + may_mount = kobj_ns_ops_tbl[type]->current_may_mount();
> + spin_unlock(&kobj_ns_type_lock);
> +
> + return may_mount;
> +}
>
> void *kobj_ns_grab_current(enum kobj_ns_type type)
> {
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 981fed3..0b0ff95 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -1157,6 +1157,13 @@ static void remove_queue_kobjects(struct net_device *net)
> #endif
> }
>
> +static bool net_current_may_mount(void)
> +{
> + struct net *net = current->nsproxy->net_ns;
> +
> + return !ns_capable(net->user_ns, CAP_SYS_ADMIN);
> +}
> +
> static void *net_grab_current_ns(void)
> {
> struct net *ns = current->nsproxy->net_ns;
> @@ -1179,6 +1186,7 @@ static const void *net_netlink_ns(struct sock *sk)
>
> struct kobj_ns_type_operations net_ns_type_operations = {
> .type = KOBJ_NS_TYPE_NET,
> + .current_may_mount = net_current_may_mount,
> .grab_current_ns = net_grab_current_ns,
> .netlink_ns = net_netlink_ns,
> .initial_ns = net_initial_ns,
>

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