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 <eescook@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>
Cc: linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, security@kernel.org
Subject: [PATCH 8/9] fs/proc: fix attr access check
Date: Sun, 18 Sep 2016 17:05:16 +0200 [thread overview]
Message-ID: <1474211117-16674-9-git-send-email-jann@thejh.net> (raw)
In-Reply-To: <1474211117-16674-1-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.
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 a9d271b..56a6cdc 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)
+{
+ u64 *opener_privunit_id;
+
+ opener_privunit_id = kmalloc(sizeof(u64), GFP_KERNEL);
+ if (opener_privunit_id == NULL)
+ return -ENOMEM;
+ *opener_privunit_id = current->self_privunit_id;
+ file->private_data = opener_privunit_id;
+ 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);
+ u64 *opener_privunit_id = 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 (*opener_privunit_id != task->self_privunit_id)
+ 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)
+{
+ u64 *opener_privunit_id = file->private_data;
+
+ kfree(opener_privunit_id);
+ 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
next prev parent reply other threads:[~2016-09-18 15:05 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-18 15:05 [PATCH 0/9] Various fixes related to ptrace_may_access() Jann Horn
2016-09-18 15:05 ` [PATCH 1/9] exec: introduce cred_guard_light Jann Horn
2016-09-18 15:05 ` [PATCH 2/9] exec: turn self_exec_id into self_privunit_id Jann Horn
2016-09-18 18:13 ` Ben Hutchings
2016-09-18 18:31 ` Jann Horn
2016-09-18 18:45 ` Ben Hutchings
2016-09-18 19:08 ` Jann Horn
2016-09-18 19:57 ` Andy Lutomirski
2016-09-19 15:31 ` Jann Horn
2016-09-18 15:05 ` [PATCH 3/9] proc: use open()-time creds for ptrace checks Jann Horn
2016-09-19 13:01 ` Stephen Smalley
2016-09-19 14:32 ` Jann Horn
2016-09-19 14:45 ` Stephen Smalley
2016-09-18 15:05 ` [PATCH 4/9] futex: don't leak robust_list pointer Jann Horn
2016-09-18 18:28 ` Ben Hutchings
2016-09-18 18:33 ` Jann Horn
2016-09-18 15:05 ` [PATCH 5/9] proc: lock properly in ptrace_may_access callers Jann Horn
2016-09-18 19:15 ` Jann Horn
2016-09-18 15:05 ` [PATCH 6/9] ptrace: warn on ptrace_may_access without proper locking Jann Horn
2016-09-18 15:05 ` [PATCH 7/9] ptrace: forbid ptrace checks against current_cred() from VFS context Jann Horn
2016-09-18 18:38 ` Ben Hutchings
2016-09-18 18:40 ` Jann Horn
2016-09-18 19:57 ` Andy Lutomirski
2016-09-18 20:38 ` Jann Horn
2016-09-18 20:18 ` Linus Torvalds
2016-09-18 20:52 ` Jann Horn
2016-09-18 15:05 ` Jann Horn [this message]
2016-09-18 15:05 ` [PATCH 9/9] Documentation: add security/ptrace_checks.txt Jann Horn
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