Re: [PATCH V2] ipc: add set_ownership() and permissions() callbacks for posix mqueue sysctl

[Christian Brauner]

On Fri, Aug 27, 2021 at 03:12:06AM -0700, CGEL wrote:
> From: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> ---

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 &current->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 &current->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
>