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From: Eric Biggers <ebiggers@kernel.org>
To: Daniel Colascione <dancol@google.com>
Cc: 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, jmorris@namei.org
Subject: Re: [PATCH v5 3/3] Wire UFFD up to SELinux
Date: Tue, 4 Aug 2020 14:16:08 -0700
Message-ID: <20200804211608.GC1992048@gmail.com> (raw)
In-Reply-To: <20200401213903.182112-4-dancol@google.com>

On Wed, Apr 01, 2020 at 02:39:03PM -0700, Daniel Colascione wrote:
> This change gives userfaultfd file descriptors a real security
> context, allowing policy to act on them.
> 
> Signed-off-by: Daniel Colascione <dancol@google.com>
> ---
>  fs/userfaultfd.c | 30 ++++++++++++++++++++++++++----
>  1 file changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 37df7c9eedb1..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;
>  };

Adding this field seems wrong.  There's no reference held to it, so it can only
be used if the caller holds a reference to the inode anyway.  The only user of
this field is via userfafultfd_read(), so why not just use the inode of the
struct file passed to userfaultfd_read()?

>  SYSCALL_DEFINE1(userfaultfd, int, flags)
>  {
> +	struct file *file;
>  	struct userfaultfd_ctx *ctx;
>  	int fd;
>  
> @@ -1974,8 +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);

What's the point of anon_inode_getfile_secure()?  anon_inode_getfd_secure()
would work here too.

- Eric

  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
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 [this message]
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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