Linux-Fsdevel Archive on lore.kernel.org
 help / color / Atom feed
From: Jann Horn <jann@thejh.net>
To: Alexander Viro <viro@zeniv.linux.org.uk>,
	Roland McGrath <roland@hack.frob.com>,
	Oleg Nesterov <oleg@redhat.com>,
	John Johansen <john.johansen@canonical.com>,
	James Morris <james.l.morris@oracle.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Paul Moore <aul@paul-moore.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	Eric Paris <eparis@parisplace.org>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Janis Danisevskis <jdanis@google.com>,
	Seth Forshee <seth.forshee@canonical.com>,
	"Eric . Biederman" <ebiederm@xmission.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Benjamin LaHaise <bcrl@kvack.org>,
	Ben Hutchings <ben@decadent.org.uk>,
	Andy Lutomirski <luto@amacapital.net>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, security@kernel.org
Subject: [PATCH v2 7/8] fs/proc: fix attr access check
Date: Fri, 23 Sep 2016 22:40:37 +0200
Message-ID: <1474663238-22134-8-git-send-email-jann@thejh.net> (raw)
In-Reply-To: <1474663238-22134-1-git-send-email-jann@thejh.net>

Make sure files in /proc/$pid/attr/ can only be written by the task that
opened them.

This prevents an attacking process from changing the security context of
another process that it can force to write attacker-controlled data into an
attacker-supplied file descriptor. I'm not sure what the impact of this is.

changed in v2:
 - changed privunit-using code

Signed-off-by: Jann Horn <jann@thejh.net>
---
 fs/proc/base.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 15845cf..27f369d 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2484,6 +2484,18 @@ out:
 }
 
 #ifdef CONFIG_SECURITY
+static int proc_pid_attr_open(struct inode *inode, struct file *file)
+{
+	struct luid *opener_privunit;
+
+	opener_privunit = kmalloc(sizeof(struct luid), GFP_KERNEL);
+	if (opener_privunit == NULL)
+		return -ENOMEM;
+	*opener_privunit = current->self_privunit;
+	file->private_data = opener_privunit;
+	return 0;
+}
+
 static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
 				  size_t count, loff_t *ppos)
 {
@@ -2512,6 +2524,7 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
 	void *page;
 	ssize_t length;
 	struct task_struct *task = get_proc_task(inode);
+	struct luid *opener_privunit = file->private_data;
 
 	length = -ESRCH;
 	if (!task)
@@ -2535,9 +2548,29 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
 	if (length < 0)
 		goto out_free;
 
+	/*
+	 * Ensure that a process can't be tricked into writing into its own attr
+	 * files without intending to do so.
+	 *
+	 * SELinux has a rule that prevents anyone other than `task` from
+	 * writing, but if the fd stays open across execve, or is sent across a
+	 * unix domain socket or whatever, that is bypassable.
+	 * Same thing in AppArmor and in Smack.
+	 *
+	 * To prevent this, compare the opener's exec_id with the target's to
+	 * ensure that they're in the same task group and no exec happened in
+	 * the meantime.
+	 *
+	 * Why is this a file and not a prctl or whatever. :/
+	 */
+	length = -EACCES;
+	if (!luid_eq(opener_privunit, &task->self_privunit))
+		goto out_unlock;
+
 	length = security_setprocattr(task,
 				      (char*)file->f_path.dentry->d_name.name,
 				      page, count);
+out_unlock:
 	mutex_unlock(&task->signal->cred_guard_mutex);
 out_free:
 	kfree(page);
@@ -2547,10 +2580,20 @@ out_no_task:
 	return length;
 }
 
+static int proc_pid_attr_release(struct inode *inode, struct file *file)
+{
+	struct luid *opener_privunit = file->private_data;
+
+	kfree(opener_privunit);
+	return 0;
+}
+
 static const struct file_operations proc_pid_attr_operations = {
+	.open		= proc_pid_attr_open,
 	.read		= proc_pid_attr_read,
 	.write		= proc_pid_attr_write,
 	.llseek		= generic_file_llseek,
+	.release	= proc_pid_attr_release,
 };
 
 static const struct pid_entry attr_dir_stuff[] = {
-- 
2.1.4


  parent reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-23 20:40 [PATCH v2 0/8] Various fixes related to ptrace_may_access() Jann Horn
2016-09-23 20:40 ` [PATCH v2 1/8] exec: introduce cred_guard_light Jann Horn
2016-09-30 15:35   ` Oleg Nesterov
2016-09-30 18:27     ` Eric W. Biederman
2016-10-03 16:02       ` Oleg Nesterov
2016-10-30 21:12     ` Jann Horn
2016-09-23 20:40 ` [PATCH v2 2/8] exec: turn self_exec_id into self_privunit Jann Horn
2016-09-23 21:04   ` Andy Lutomirski
2016-09-23 21:33     ` Jann Horn
2016-09-30 13:20   ` Oleg Nesterov
2016-09-30 13:44     ` Oleg Nesterov
2016-09-30 18:30       ` Kees Cook
2016-09-30 18:59         ` Jann Horn
2016-09-30 19:05           ` Kees Cook
2016-10-03 16:37         ` Oleg Nesterov
2016-09-23 20:40 ` [PATCH v2 3/8] proc: use open()-time creds for ptrace checks Jann Horn
2016-09-23 20:40 ` [PATCH v2 4/8] futex: don't leak robust_list pointer Jann Horn
2016-09-30 14:52   ` Oleg Nesterov
2016-10-30 17:16     ` Jann Horn
2016-11-02 21:39       ` Jann Horn
2016-11-02 22:47         ` Jann Horn
2016-09-23 20:40 ` [PATCH v2 5/8] proc: lock properly in ptrace_may_access callers Jann Horn
2016-09-23 20:40 ` [PATCH v2 6/8] ptrace: warn on ptrace_may_access without proper locking Jann Horn
2016-09-23 20:40 ` Jann Horn [this message]
2016-09-23 20:40 ` [PATCH v2 8/8] Documentation: add security/ptrace_checks.txt Jann Horn
2016-10-02  3:16   ` Krister Johansen
2016-10-30 19:09     ` Jann Horn
2016-10-31  4:14       ` Eric W. Biederman
2016-10-31 13:39         ` Jann Horn
2016-11-03 20:43         ` Krister Johansen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1474663238-22134-8-git-send-email-jann@thejh.net \
    --to=jann@thejh.net \
    --cc=akpm@linux-foundation.org \
    --cc=aul@paul-moore.com \
    --cc=bcrl@kvack.org \
    --cc=ben@decadent.org.uk \
    --cc=casey@schaufler-ca.com \
    --cc=ebiederm@xmission.com \
    --cc=eparis@parisplace.org \
    --cc=james.l.morris@oracle.com \
    --cc=jdanis@google.com \
    --cc=john.johansen@canonical.com \
    --cc=keescook@chromium.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=luto@amacapital.net \
    --cc=oleg@redhat.com \
    --cc=roland@hack.frob.com \
    --cc=sds@tycho.nsa.gov \
    --cc=security@kernel.org \
    --cc=serge@hallyn.com \
    --cc=seth.forshee@canonical.com \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linux-foundation.org \
    --cc=viro@zeniv.linux.org.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Fsdevel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-fsdevel/0 linux-fsdevel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-fsdevel linux-fsdevel/ https://lore.kernel.org/linux-fsdevel \
		linux-fsdevel@vger.kernel.org
	public-inbox-index linux-fsdevel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-fsdevel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git