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From: Casey Schaufler <casey@schaufler-ca.com>
To: Daniel Colascione <dancol@google.com>,
	timmurray@google.com, selinux@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, viro@zeniv.linux.org.uk,
	paul@paul-moore.com, nnk@google.com, sds@tycho.nsa.gov,
	lokeshgidra@google.com, Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: [PATCH v2 3/3] Wire UFFD up to SELinux
Date: Wed, 25 Mar 2020 16:49:14 -0700
Message-ID: <a8d0938c-6ab5-0323-8e98-35e7d3232282@schaufler-ca.com> (raw)
In-Reply-To: <20200325230245.184786-4-dancol@google.com>

On 3/25/2020 4:02 PM, Daniel Colascione wrote:
> This change gives userfaultfd file descriptors a real security
> context, allowing policy to act on them.

You should change the title to "Wire UFFD up to secure anon inodes".
This code should support any LSM that wants to control anon inodes.
If it doesn't, it isn't correct.

All references to SELinux behavior (i.e. assigning a "security context")
should be restricted to the SELinux specific bits of the patch set. You
should be describing how any LSM can use this, not just the LSM you've
targeted.

>
> Signed-off-by: Daniel Colascione <dancol@google.com>
> ---
>  fs/userfaultfd.c | 34 +++++++++++++++++++++++++++++-----
>  1 file changed, 29 insertions(+), 5 deletions(-)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 07b0f6e03849..78ff5d898733 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -76,6 +76,8 @@ struct userfaultfd_ctx {
>  	bool mmap_changing;
>  	/* mm with one ore more vmas attached to this userfaultfd_ctx */
>  	struct mm_struct *mm;
> +	/* The inode that owns this context --- not a strong reference.  */
> +	const struct inode *owner;
>  };
>  
>  struct userfaultfd_fork_ctx {
> @@ -1014,14 +1016,18 @@ static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
>  	}
>  }
>  
> +static const struct file_operations userfaultfd_fops;
> +
>  static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
>  				  struct userfaultfd_ctx *new,
>  				  struct uffd_msg *msg)
>  {
>  	int fd;
>  
> -	fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, new,
> -			      O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS));
> +	fd = anon_inode_getfd_secure(
> +		"[userfaultfd]", &userfaultfd_fops, new,
> +		O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS),
> +		ctx->owner);
>  	if (fd < 0)
>  		return fd;
>  
> @@ -1918,7 +1924,7 @@ static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
>  }
>  #endif
>  
> -const struct file_operations userfaultfd_fops = {
> +static const struct file_operations userfaultfd_fops = {
>  #ifdef CONFIG_PROC_FS
>  	.show_fdinfo	= userfaultfd_show_fdinfo,
>  #endif
> @@ -1943,6 +1949,7 @@ static void init_once_userfaultfd_ctx(void *mem)
>  
>  SYSCALL_DEFINE1(userfaultfd, int, flags)
>  {
> +	struct file *file;
>  	struct userfaultfd_ctx *ctx;
>  	int fd;
>  
> @@ -1972,8 +1979,25 @@ SYSCALL_DEFINE1(userfaultfd, int, flags)
>  	/* prevent the mm struct to be freed */
>  	mmgrab(ctx->mm);
>  
> -	fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
> -			      O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
> +	file = anon_inode_getfile_secure(
> +		"[userfaultfd]", &userfaultfd_fops, ctx,
> +		O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS),
> +		NULL);
> +	if (IS_ERR(file)) {
> +		fd = PTR_ERR(file);
> +		goto out;
> +	}
> +
> +	fd = get_unused_fd_flags(O_RDONLY | O_CLOEXEC);
> +	if (fd < 0) {
> +		fput(file);
> +		goto out;
> +	}
> +
> +	ctx->owner = file_inode(file);
> +	fd_install(fd, file);
> +
> +out:
>  	if (fd < 0) {
>  		mmdrop(ctx->mm);
>  		kmem_cache_free(userfaultfd_ctx_cachep, ctx);


  reply index

Thread overview: 80+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-11 22:55 [PATCH v2 0/6] Harden userfaultfd Daniel Colascione
2020-02-11 22:55 ` [PATCH v2 1/6] Add a new flags-accepting interface for anonymous inodes Daniel Colascione
2020-02-12 16:37   ` Stephen Smalley
2020-02-12 17:23     ` Daniel Colascione
2020-02-11 22:55 ` [PATCH v2 2/6] Add a concept of a "secure" anonymous file Daniel Colascione
2020-02-12 16:49   ` Stephen Smalley
2020-02-14 22:13   ` kbuild test robot
2020-02-11 22:55 ` [PATCH v2 3/6] Teach SELinux about a new userfaultfd class Daniel Colascione
2020-02-12 17:05   ` Stephen Smalley
2020-02-12 17:19     ` Daniel Colascione
2020-02-12 18:04       ` Stephen Smalley
2020-02-12 18:59         ` Stephen Smalley
2020-02-12 19:04           ` Daniel Colascione
2020-02-12 19:11             ` Stephen Smalley
2020-02-12 19:13               ` Daniel Colascione
2020-02-12 19:17               ` Stephen Smalley
2020-02-11 22:55 ` [PATCH v2 4/6] Wire UFFD up to SELinux Daniel Colascione
2020-02-11 22:55 ` [PATCH v2 5/6] Let userfaultfd opt out of handling kernel-mode faults Daniel Colascione
2020-02-11 22:55 ` [PATCH v2 6/6] Add a new sysctl for limiting userfaultfd to user mode faults Daniel Colascione
2020-02-11 23:13 ` [PATCH v2 0/6] Harden userfaultfd Casey Schaufler
2020-02-11 23:27   ` Daniel Colascione
2020-02-12 16:09     ` Stephen Smalley
2020-02-21 17:56     ` James Morris
2020-02-12  7:50 ` Kees Cook
2020-02-12 16:54   ` Jann Horn
2020-02-12 17:14     ` Peter Xu
2020-02-12 19:41       ` Andrea Arcangeli
2020-02-12 20:04         ` Daniel Colascione
2020-02-12 23:41           ` Andrea Arcangeli
2020-02-12 17:12   ` Daniel Colascione
2020-02-14  3:26 ` [PATCH 0/3] SELinux support for anonymous inodes and UFFD Daniel Colascione
2020-02-14  3:26   ` [PATCH 1/3] Add a new LSM-supporting anonymous inode interface Daniel Colascione
2020-02-14  3:26   ` [PATCH 2/3] Teach SELinux about anonymous inodes Daniel Colascione
2020-02-14 16:39     ` Stephen Smalley
2020-02-14 17:21       ` Daniel Colascione
2020-02-14 18:02         ` Stephen Smalley
2020-02-14 18:08           ` Stephen Smalley
2020-02-14 20:24             ` Stephen Smalley
2020-02-14  3:26   ` [PATCH 3/3] Wire UFFD up to SELinux Daniel Colascione
2020-03-25 23:02   ` [PATCH v2 0/3] SELinux support for anonymous inodes and UFFD Daniel Colascione
2020-03-25 23:02   ` [PATCH v2 1/3] Add a new LSM-supporting anonymous inode interface Daniel Colascione
2020-03-26 13:53     ` Stephen Smalley
2020-03-25 23:02   ` [PATCH v2 2/3] Teach SELinux about anonymous inodes Daniel Colascione
2020-03-26 13:58     ` Stephen Smalley
2020-03-26 17:59       ` Daniel Colascione
2020-03-26 17:37     ` Stephen Smalley
2020-03-25 23:02   ` [PATCH v2 3/3] Wire UFFD up to SELinux Daniel Colascione
2020-03-25 23:49     ` Casey Schaufler [this message]
2020-03-26 18:14   ` [PATCH v3 0/3] SELinux support for anonymous inodes and UFFD Daniel Colascione
2020-03-26 18:14     ` [PATCH v3 1/3] Add a new LSM-supporting anonymous inode interface Daniel Colascione
2020-03-26 19:00       ` Stephen Smalley
2020-03-26 18:14     ` [PATCH v3 2/3] Teach SELinux about anonymous inodes Daniel Colascione
2020-03-26 19:02       ` Stephen Smalley
2020-03-26 18:14     ` [PATCH v3 3/3] Wire UFFD up to SELinux Daniel Colascione
2020-03-26 20:06     ` [PATCH v4 0/3] SELinux support for anonymous inodes and UFFD Daniel Colascione
2020-03-26 20:06       ` [PATCH v4 1/3] Add a new LSM-supporting anonymous inode interface Daniel Colascione
2020-03-27 13:40         ` Stephen Smalley
2020-03-26 20:06       ` [PATCH v4 2/3] Teach SELinux about anonymous inodes Daniel Colascione
2020-03-27 13:41         ` Stephen Smalley
2020-03-26 20:06       ` [PATCH v4 3/3] Wire UFFD up to SELinux Daniel Colascione
2020-04-01 21:39       ` [PATCH v5 0/3] SELinux support for anonymous inodes and UFFD Daniel Colascione
2020-04-01 21:39         ` [PATCH v5 1/3] Add a new LSM-supporting anonymous inode interface Daniel Colascione
2020-05-07 16:02           ` James Morris
2020-08-04 21:22           ` Eric Biggers
2020-04-01 21:39         ` [PATCH v5 2/3] Teach SELinux about anonymous inodes Daniel Colascione
2020-04-01 21:39         ` [PATCH v5 3/3] Wire UFFD up to SELinux Daniel Colascione
2020-08-04 21:16           ` Eric Biggers
2020-04-13 13:29         ` [PATCH v5 0/3] SELinux support for anonymous inodes and UFFD Daniel Colascione
2020-04-22 16:55           ` James Morris
2020-04-22 17:12             ` Casey Schaufler
2020-04-23 22:24               ` Casey Schaufler
2020-04-27 16:18                 ` Casey Schaufler
2020-04-27 16:48                   ` Stephen Smalley
2020-04-27 17:12                     ` Casey Schaufler
2020-04-29 17:02                     ` Stephen Smalley
2020-04-27 17:15             ` Casey Schaufler
2020-04-27 19:40               ` Stephen Smalley
2020-06-04  3:56         ` James Morris
2020-06-04 18:51           ` Stephen Smalley
2020-06-04 19:24             ` Lokesh Gidra

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