linux-kernel - Re: [PATCH 1/1 V2] mqueue: Implment generic xattr support

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Date:   Mon, 7 Nov 2016 17:23:46 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     David Graziano <david.graziano@...kwellcollins.com>
Cc:     golbi@....uni.torun.pl, michal.wronski@...il.com,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Stephen Smalley <sds@...ho.nsa.gov>,
        seth.forshee@...onical.com, ebiederm@...ssion.com,
        selinux@...ho.nsa.gov
Subject: Re: [PATCH 1/1 V2] mqueue: Implment generic xattr support

On Mon, Nov 7, 2016 at 3:46 PM, David Graziano
<david.graziano@...kwellcollins.com> wrote:
> This patch adds support for generic extended attributes within the
> POSIX message queues filesystem and setting them by consulting the LSM.
> This is needed so that the security.selinux extended attribute can be
> set via a SELinux named type transition on file inodes created within
> the filesystem. The implementation and LSM call back function are based
> off tmpfs/shmem.
>
> Signed-off-by: David Graziano <david.graziano@...kwellcollins.com>
> ---
>  ipc/mqueue.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)

Hi David,

At first glance this looks reasonable to me, I just have a two
questions/comments:

* Can you explain your current need for this functionality?  For
example, what are you trying to do that is made easier by allowing
greater message queue labeling flexibility?  This helps put things in
context and helps people review and comment on your patch.

* How have you tested this?  While this patch is not SELinux specific,
I think adding a test to the selinux-testsuite[1] would be worthwhile.
The other LSM maintainers may suggest something similar if they have
an established public testsuite.

[1] https://github.com/SELinuxProject/selinux-testsuite

> diff --git a/ipc/mqueue.c b/ipc/mqueue.c
> index 0b13ace..512a546 100644
> --- a/ipc/mqueue.c
> +++ b/ipc/mqueue.c
> @@ -35,6 +35,7 @@
>  #include <linux/ipc_namespace.h>
>  #include <linux/user_namespace.h>
>  #include <linux/slab.h>
> +#include <linux/xattr.h>
>
>  #include <net/sock.h>
>  #include "util.h"
> @@ -70,6 +71,7 @@ struct mqueue_inode_info {
>         struct rb_root msg_tree;
>         struct posix_msg_tree_node *node_cache;
>         struct mq_attr attr;
> +       struct simple_xattrs xattrs;    /* list of xattrs */
>
>         struct sigevent notify;
>         struct pid *notify_owner;
> @@ -254,6 +256,7 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
>                         info->attr.mq_maxmsg = attr->mq_maxmsg;
>                         info->attr.mq_msgsize = attr->mq_msgsize;
>                 }
> +               simple_xattrs_init(&info->xattrs);
>                 /*
>                  * We used to allocate a static array of pointers and account
>                  * the size of that array as well as one msg_msg struct per
> @@ -413,6 +416,41 @@ static void mqueue_evict_inode(struct inode *inode)
>                 put_ipc_ns(ipc_ns);
>  }
>
> +/*
> + * Callback for security_inode_init_security() for acquiring xattrs.
> + */
> +static int mqueue_initxattrs(struct inode *inode,
> +                           const struct xattr *xattr_array,
> +                           void *fs_info)
> +{
> +       struct mqueue_inode_info *info = MQUEUE_I(inode);
> +       const struct xattr *xattr;
> +       struct simple_xattr *new_xattr;
> +       size_t len;
> +
> +       for (xattr = xattr_array; xattr->name != NULL; xattr++) {
> +               new_xattr = simple_xattr_alloc(xattr->value, xattr->value_len);
> +               if (!new_xattr)
> +                       return -ENOMEM;
> +               len = strlen(xattr->name) + 1;
> +               new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
> +                                         GFP_KERNEL);
> +               if (!new_xattr->name) {
> +                       kfree(new_xattr);
> +                       return -ENOMEM;
> +               }
> +
> +               memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
> +                      XATTR_SECURITY_PREFIX_LEN);
> +               memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
> +                      xattr->name, len);
> +
> +               simple_xattr_list_add(&info->xattrs, new_xattr);
> +       }
> +
> +       return 0;
> +}
> +
>  static int mqueue_create(struct inode *dir, struct dentry *dentry,
>                                 umode_t mode, bool excl)
>  {
> @@ -443,6 +481,14 @@ static int mqueue_create(struct inode *dir, struct dentry *dentry,
>                 ipc_ns->mq_queues_count--;
>                 goto out_unlock;
>         }
> +       error = security_inode_init_security(inode, dir,
> +                                            &dentry->d_name,
> +                                            mqueue_initxattrs, NULL);
> +       if (error && error != -EOPNOTSUPP) {
> +               spin_lock(&mq_lock);
> +               ipc_ns->mq_queues_count--;
> +               goto out_unlock;
> +       }
>
>         put_ipc_ns(ipc_ns);
>         dir->i_size += DIRENT_SIZE;
> --
> 1.9.1
>
> --
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-- 
paul moore
www.paul-moore.com