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 W. 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>,
Krister Johansen <kjlx@templeofstupid.com>
Cc: linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, security@kernel.org
Subject: [PATCH v3 6/8] fs/proc: fix attr access check
Date: Sun, 30 Oct 2016 22:46:36 +0100 [thread overview]
Message-ID: <1477863998-3298-7-git-send-email-jann@thejh.net> (raw)
In-Reply-To: <1477863998-3298-1-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 32ea9bc3d320..cbba490543e2 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2518,6 +2518,18 @@ static int proc_pident_readdir(struct file *file, struct dir_context *ctx,
}
#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->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)
{
@@ -2546,6 +2558,7 @@ 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)
@@ -2569,9 +2582,29 @@ 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->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);
@@ -2581,10 +2614,20 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
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
next prev parent reply other threads:[~2016-10-30 21:46 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-30 21:46 [PATCH v3 0/8] Various fixes related to ptrace_may_access() Jann Horn
2016-10-30 21:46 ` [PATCH v3 1/8] exec: introduce cred_guard_light Jann Horn
2016-11-02 18:18 ` Oleg Nesterov
2016-11-02 20:50 ` Jann Horn
2016-11-02 21:38 ` Ben Hutchings
2016-11-02 21:54 ` Jann Horn
2016-11-03 18:12 ` Oleg Nesterov
2016-11-03 21:17 ` Jann Horn
2016-11-04 13:26 ` Eric W. Biederman
2016-11-04 15:00 ` Eric W. Biederman
2016-11-04 18:04 ` Oleg Nesterov
2016-11-04 18:45 ` Oleg Nesterov
2016-11-05 14:56 ` Oleg Nesterov
2016-11-09 0:34 ` Eric W. Biederman
2016-11-16 20:03 ` Eric W. Biederman
2016-11-08 22:02 ` Kees Cook
2016-11-08 22:46 ` Eric W. Biederman
2016-11-08 22:56 ` Benjamin LaHaise
2016-11-08 23:33 ` Eric W. Biederman
2016-10-30 21:46 ` [PATCH v3 2/8] exec: add privunit to task_struct Jann Horn
2016-10-30 21:46 ` [PATCH v3 3/8] proc: use open()-time creds for ptrace checks Jann Horn
2016-10-30 21:46 ` [PATCH v3 4/8] futex: don't leak robust_list pointer Jann Horn
2016-10-30 21:46 ` [PATCH v3 5/8] proc: lock properly in ptrace_may_access callers Jann Horn
2016-10-30 21:46 ` Jann Horn [this message]
2016-10-30 21:46 ` [PATCH v3 7/8] proc: fix timerslack_ns handling Jann Horn
2016-10-30 21:46 ` [PATCH v3 8/8] Documentation: add security/ptrace_checks.txt Jann Horn
2016-11-01 23:57 ` [PATCH v3 0/8] Various fixes related to ptrace_may_access() Linus Torvalds
2016-11-02 18:38 ` Oleg Nesterov
2016-11-02 21:40 ` Jann Horn
2016-11-03 19:09 ` Andrew Morton
2016-11-03 20:01 ` Jann Horn
2016-11-04 0:57 ` James Morris
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