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Date: Mon, 13 Sep 2021 16:40:47 +0200
From: Christian Brauner <christian.brauner@...ntu.com>
To: dbueso@...e.de
Cc: CGEL <cgel.zte@...il.com>, jamorris@...ux.microsoft.com,
keescook@...omium.org, ktkhai@...tuozzo.com, legion@...nel.org,
linux-kernel@...r.kernel.org, ran.xiaokai@....com.cn,
varad.gautam@...e.com
Subject: Re: [PATCH V2] ipc: add set_ownership() and permissions() callbacks
for posix mqueue sysctl
On Fri, Aug 27, 2021 at 03:12:06AM -0700, CGEL wrote:
> From: Ran Xiaokai <ran.xiaokai@....com.cn>
>
> When a non-root user process creates a user namespace and ipc namespace
> with command "unshare -Ur -i", and map the root user inside
> the user namesapce to the global owner of user namespace.
> The newly created user namespace OWNS the ipc namespace,
> So the root user inside the user namespace should have full access
> rights to the ipc namespace resources and should be writable to
> the ipc mqueue sysctls.
>
> v2:
> - update commit msg.
> - fix the coding style issue.
> Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
> ---
David,
are you happy with this too? If so I'd pick this up.
> include/linux/ipc_namespace.h | 14 +++++
> ipc/mq_sysctl.c | 118 ++++++++++++++++++++++++++++++++++++------
> ipc/mqueue.c | 10 +++-
> ipc/namespace.c | 2 +
> 4 files changed, 126 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
> index 05e2277..3e8e340 100644
> --- a/include/linux/ipc_namespace.h
> +++ b/include/linux/ipc_namespace.h
> @@ -10,6 +10,7 @@
> #include <linux/ns_common.h>
> #include <linux/refcount.h>
> #include <linux/rhashtable-types.h>
> +#include <linux/sysctl.h>
>
> struct user_namespace;
>
> @@ -67,6 +68,11 @@ struct ipc_namespace {
> struct user_namespace *user_ns;
> struct ucounts *ucounts;
>
> +#ifdef CONFIG_POSIX_MQUEUE_SYSCTL
> + struct ctl_table_set mq_set;
> + struct ctl_table_header *sysctls;
> +#endif
> +
> struct llist_node mnt_llist;
>
> struct ns_common ns;
> @@ -155,7 +161,10 @@ static inline void put_ipc_ns(struct ipc_namespace *ns)
> #ifdef CONFIG_POSIX_MQUEUE_SYSCTL
>
> struct ctl_table_header;
> +extern struct ctl_table_header *mq_sysctl_table;
> extern struct ctl_table_header *mq_register_sysctl_table(void);
> +bool setup_mq_sysctls(struct ipc_namespace *ns);
> +void retire_mq_sysctls(struct ipc_namespace *ns);
>
> #else /* CONFIG_POSIX_MQUEUE_SYSCTL */
>
> @@ -163,6 +172,11 @@ static inline struct ctl_table_header *mq_register_sysctl_table(void)
> {
> return NULL;
> }
> +static inline bool setup_mq_sysctls(struct ipc_namespace *ns)
> +{
> + return true;
> +}
> +static inline void retire_mq_sysctls(struct ipc_namespace *ns) { }
>
> #endif /* CONFIG_POSIX_MQUEUE_SYSCTL */
> #endif
> diff --git a/ipc/mq_sysctl.c b/ipc/mq_sysctl.c
> index 72a92a0..8d6b8ff 100644
> --- a/ipc/mq_sysctl.c
> +++ b/ipc/mq_sysctl.c
> @@ -8,6 +8,11 @@
> #include <linux/nsproxy.h>
> #include <linux/ipc_namespace.h>
> #include <linux/sysctl.h>
> +#include <linux/slab.h>
> +#include <linux/user_namespace.h>
> +#include <linux/capability.h>
> +#include <linux/cred.h>
> +#include <linux/stat.h>
>
> #ifdef CONFIG_PROC_SYSCTL
> static void *get_mq(struct ctl_table *table)
> @@ -96,25 +101,106 @@ static struct ctl_table mq_sysctls[] = {
> {}
> };
>
> -static struct ctl_table mq_sysctl_dir[] = {
> - {
> - .procname = "mqueue",
> - .mode = 0555,
> - .child = mq_sysctls,
> - },
> - {}
> -};
> +static int set_is_seen(struct ctl_table_set *set)
> +{
> + return ¤t->nsproxy->ipc_ns->mq_set == set;
> +}
>
> -static struct ctl_table mq_sysctl_root[] = {
> - {
> - .procname = "fs",
> - .mode = 0555,
> - .child = mq_sysctl_dir,
> - },
> - {}
> +static struct ctl_table_set *
> +set_lookup(struct ctl_table_root *root)
> +{
> + return ¤t->nsproxy->ipc_ns->mq_set;
> +}
> +
> +static int set_permissions(struct ctl_table_header *head,
> + struct ctl_table *table)
> +{
> + struct ipc_namespace *ipc_ns =
> + container_of(head->set, struct ipc_namespace, mq_set);
> + struct user_namespace *user_ns = ipc_ns->user_ns;
> + int mode;
> +
> + /* Allow users with CAP_SYS_RESOURCE unrestrained access */
> + if (ns_capable(user_ns, CAP_SYS_RESOURCE))
> + mode = (table->mode & S_IRWXU) >> 6;
> + else {
> + /* Allow all others at most read-only access */
> + mode = table->mode & S_IROTH;
> + }
> +
> + return (mode << 6) | (mode << 3) | mode;
> +}
> +
> +static void set_ownership(struct ctl_table_header *head,
> + struct ctl_table *table,
> + kuid_t *uid, kgid_t *gid)
> +{
> + struct ipc_namespace *ipc_ns =
> + container_of(head->set, struct ipc_namespace, mq_set);
> + struct user_namespace *user_ns = ipc_ns->user_ns;
> + kuid_t ns_root_uid;
> + kgid_t ns_root_gid;
> +
> + ns_root_uid = make_kuid(user_ns, 0);
> + if (uid_valid(ns_root_uid))
> + *uid = ns_root_uid;
> +
> + ns_root_gid = make_kgid(user_ns, 0);
> + if (gid_valid(ns_root_gid))
> + *gid = ns_root_gid;
> +}
> +
> +static struct ctl_table_root mq_sysctl_root = {
> + .lookup = set_lookup,
> + .permissions = set_permissions,
> + .set_ownership = set_ownership,
> };
>
> +bool setup_mq_sysctls(struct ipc_namespace *ns)
> +{
> + struct ctl_table *tbl;
> +
> + if (!mq_sysctl_table)
> + return false;
> +
> + setup_sysctl_set(&ns->mq_set, &mq_sysctl_root, set_is_seen);
> + tbl = kmemdup(mq_sysctls, sizeof(mq_sysctls), GFP_KERNEL);
> + if (!tbl)
> + goto out;
> +
> + ns->sysctls = __register_sysctl_table(&ns->mq_set, "fs/mqueue", tbl);
> + if (!ns->sysctls)
> + goto out1;
> +
> + return true;
> +
> +out1:
> + kfree(tbl);
> + retire_sysctl_set(&ns->mq_set);
> +out:
> + return false;
> +}
> +
> +void retire_mq_sysctls(struct ipc_namespace *ns)
> +{
> + struct ctl_table *tbl;
> +
> + if (!ns->sysctls)
> + return;
> +
> + tbl = ns->sysctls->ctl_table_arg;
> + unregister_sysctl_table(ns->sysctls);
> + retire_sysctl_set(&ns->mq_set);
> + kfree(tbl);
> +}
> +
> struct ctl_table_header *mq_register_sysctl_table(void)
> {
> - return register_sysctl_table(mq_sysctl_root);
> + static struct ctl_table empty[1];
> +
> + /*
> + * Register the fs/mqueue directory in the default set so that
> + * registrations in the child sets work properly.
> + */
> + return register_sysctl("fs/mqueue", empty);
> }
> diff --git a/ipc/mqueue.c b/ipc/mqueue.c
> index 4e4e611..3b68564 100644
> --- a/ipc/mqueue.c
> +++ b/ipc/mqueue.c
> @@ -163,7 +163,7 @@ static void remove_notification(struct mqueue_inode_info *info);
>
> static struct kmem_cache *mqueue_inode_cachep;
>
> -static struct ctl_table_header *mq_sysctl_table;
> +struct ctl_table_header *mq_sysctl_table;
>
> static inline struct mqueue_inode_info *MQUEUE_I(struct inode *inode)
> {
> @@ -1713,6 +1713,10 @@ static int __init init_mqueue_fs(void)
>
> /* ignore failures - they are not fatal */
> mq_sysctl_table = mq_register_sysctl_table();
> + if (mq_sysctl_table && !setup_mq_sysctls(&init_ipc_ns)) {
> + unregister_sysctl_table(mq_sysctl_table);
> + mq_sysctl_table = NULL;
> + }
>
> error = register_filesystem(&mqueue_fs_type);
> if (error)
> @@ -1729,8 +1733,10 @@ static int __init init_mqueue_fs(void)
> out_filesystem:
> unregister_filesystem(&mqueue_fs_type);
> out_sysctl:
> - if (mq_sysctl_table)
> + if (mq_sysctl_table) {
> + retire_mq_sysctls(&init_ipc_ns);
> unregister_sysctl_table(mq_sysctl_table);
> + }
> kmem_cache_destroy(mqueue_inode_cachep);
> return error;
> }
> diff --git a/ipc/namespace.c b/ipc/namespace.c
> index 7bd0766..c891cc1 100644
> --- a/ipc/namespace.c
> +++ b/ipc/namespace.c
> @@ -58,6 +58,7 @@ static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
> err = mq_init_ns(ns);
> if (err)
> goto fail_put;
> + setup_mq_sysctls(ns);
>
> sem_init_ns(ns);
> msg_init_ns(ns);
> @@ -121,6 +122,7 @@ static void free_ipc_ns(struct ipc_namespace *ns)
> * uses synchronize_rcu().
> */
> mq_put_mnt(ns);
> + retire_mq_sysctls(ns);
> sem_exit_ns(ns);
> msg_exit_ns(ns);
> shm_exit_ns(ns);
> --
> 2.15.2
>
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