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Commit 522ed776 authored by Miloslav Trmac's avatar Miloslav Trmac Committed by Linus Torvalds
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Audit: add TTY input auditing 

Add TTY input auditing, used to audit system administrator's actions.  This is
required by various security standards such as DCID 6/3 and PCI to provide
non-repudiation of administrator's actions and to allow a review of past
actions if the administrator seems to overstep their duties or if the system
becomes misconfigured for unknown reasons.  These requirements do not make it
necessary to audit TTY output as well.

Compared to an user-space keylogger, this approach records TTY input using the
audit subsystem, correlated with other audit events, and it is completely
transparent to the user-space application (e.g.  the console ioctls still
work).

TTY input auditing works on a higher level than auditing all system calls
within the session, which would produce an overwhelming amount of mostly
useless audit events.

Add an "audit_tty" attribute, inherited across fork ().  Data read from TTYs
by process with the attribute is sent to the audit subsystem by the kernel.
The audit netlink interface is extended to allow modifying the audit_tty
attribute, and to allow sending explanatory audit events from user-space (for
example, a shell might send an event containing the final command, after the
interactive command-line editing and history expansion is performed, which
might be difficult to decipher from the TTY input alone).

Because the "audit_tty" attribute is inherited across fork (), it would be set
e.g.  for sshd restarted within an audited session.  To prevent this, the
audit_tty attribute is cleared when a process with no open TTY file
descriptors (e.g.  after daemon startup) opens a TTY.

See https://www.redhat.com/archives/linux-audit/2007-June/msg00000.html

 for a
more detailed rationale document for an older version of this patch.

[akpm@linux-foundation.org: build fix]
Signed-off-by: default avatarMiloslav Trmac <mitr@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Paul Fulghum <paulkf@microgate.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: Steve Grubb <sgrubb@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4f27c00b

drivers/char/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ obj-y += misc.o 
obj-$(CONFIG_VT)		+= vt_ioctl.o vc_screen.o consolemap.o \

				   consolemap_deftbl.o selection.o keyboard.o

obj-$(CONFIG_HW_CONSOLE)	+= vt.o defkeymap.o

obj-$(CONFIG_AUDIT)		+= tty_audit.o

obj-$(CONFIG_MAGIC_SYSRQ)	+= sysrq.o

obj-$(CONFIG_ESPSERIAL)		+= esp.o

obj-$(CONFIG_MVME147_SCC)	+= generic_serial.o vme_scc.o

drivers/char/n_tty.c

+16 −4
Original line number Diff line number Diff line
@@ -45,6 +45,8 @@ 
#include <linux/slab.h>

#include <linux/poll.h>

#include <linux/bitops.h>

#include <linux/audit.h>

#include <linux/file.h>



#include <asm/uaccess.h>

#include <asm/system.h>
@@ -78,6 +80,13 @@ static inline void free_buf(unsigned char *buf) 
		free_page((unsigned long) buf);

}



static inline int tty_put_user(struct tty_struct *tty, unsigned char x,

			       unsigned char __user *ptr)

{

	tty_audit_add_data(tty, &x, 1);

	return put_user(x, ptr);

}



/**

 *	n_tty_set__room	-	receive space

 *	@tty: terminal
@@ -1153,6 +1162,7 @@ static int copy_from_read_buf(struct tty_struct *tty, 
	if (n) {

		retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);

		n -= retval;

		tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);

		spin_lock_irqsave(&tty->read_lock, flags);

		tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);

		tty->read_cnt -= n;
@@ -1279,7 +1289,7 @@ do_it_again: 
				break;

			cs = tty->link->ctrl_status;

			tty->link->ctrl_status = 0;

			if (put_user(cs, b++)) {

			if (tty_put_user(tty, cs, b++)) {

				retval = -EFAULT;

				b--;

				break;
@@ -1321,7 +1331,7 @@ do_it_again: 


		/* Deal with packet mode. */

		if (tty->packet && b == buf) {

			if (put_user(TIOCPKT_DATA, b++)) {

			if (tty_put_user(tty, TIOCPKT_DATA, b++)) {

				retval = -EFAULT;

				b--;

				break;
@@ -1352,16 +1362,18 @@ do_it_again: 
				spin_unlock_irqrestore(&tty->read_lock, flags);



				if (!eol || (c != __DISABLED_CHAR)) {

					if (put_user(c, b++)) {

					if (tty_put_user(tty, c, b++)) {

						retval = -EFAULT;

						b--;

						break;

					}

					nr--;

				}

				if (eol)

				if (eol) {

					tty_audit_push(tty);

					break;

				}

			}

			if (retval)

				break;

		} else {

drivers/char/tty_audit.c

0 → 100644
+345 −0
Original line number Diff line number Diff line 
/*

 * Creating audit events from TTY input.

 *

 * Copyright (C) 2007 Red Hat, Inc.  All rights reserved.  This copyrighted

 * material is made available to anyone wishing to use, modify, copy, or

 * redistribute it subject to the terms and conditions of the GNU General

 * Public License v.2.

 *

 * Authors: Miloslav Trmac <mitr@redhat.com>

 */



#include <linux/audit.h>

#include <linux/file.h>

#include <linux/tty.h>



struct tty_audit_buf {

	atomic_t count;

	struct mutex mutex;	/* Protects all data below */

	int major, minor;	/* The TTY which the data is from */

	unsigned icanon:1;

	size_t valid;

	unsigned char *data;	/* Allocated size N_TTY_BUF_SIZE */

};



static struct tty_audit_buf *tty_audit_buf_alloc(int major, int minor,

						 int icanon)

{

	struct tty_audit_buf *buf;



	buf = kmalloc(sizeof (*buf), GFP_KERNEL);

	if (!buf)

		goto err;

	if (PAGE_SIZE != N_TTY_BUF_SIZE)

		buf->data = kmalloc(N_TTY_BUF_SIZE, GFP_KERNEL);

	else

		buf->data = (unsigned char *)__get_free_page(GFP_KERNEL);

	if (!buf->data)

		goto err_buf;

	atomic_set(&buf->count, 1);

	mutex_init(&buf->mutex);

	buf->major = major;

	buf->minor = minor;

	buf->icanon = icanon;

	buf->valid = 0;

	return buf;



err_buf:

	kfree(buf);

err:

	return NULL;

}



static void tty_audit_buf_free(struct tty_audit_buf *buf)

{

	WARN_ON(buf->valid != 0);

	if (PAGE_SIZE != N_TTY_BUF_SIZE)

		kfree(buf->data);

	else

		free_page((unsigned long)buf->data);

	kfree(buf);

}



static void tty_audit_buf_put(struct tty_audit_buf *buf)

{

	if (atomic_dec_and_test(&buf->count))

		tty_audit_buf_free(buf);

}



/**

 *	tty_audit_buf_push	-	Push buffered data out

 *

 *	Generate an audit message from the contents of @buf, which is owned by

 *	@tsk with @loginuid.  @buf->mutex must be locked.

 */

static void tty_audit_buf_push(struct task_struct *tsk, uid_t loginuid,

			       struct tty_audit_buf *buf)

{

	struct audit_buffer *ab;



	if (buf->valid == 0)

		return;

	if (audit_enabled == 0)

		return;

	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_TTY);

	if (ab) {

		char name[sizeof(tsk->comm)];



		audit_log_format(ab, "tty pid=%u uid=%u auid=%u major=%d "

				 "minor=%d comm=", tsk->pid, tsk->uid,

				 loginuid, buf->major, buf->minor);

		get_task_comm(name, tsk);

		audit_log_untrustedstring(ab, name);

		audit_log_format(ab, " data=");

		audit_log_n_untrustedstring(ab, buf->valid, buf->data);

		audit_log_end(ab);

	}

	buf->valid = 0;

}



/**

 *	tty_audit_buf_push_current	-	Push buffered data out

 *

 *	Generate an audit message from the contents of @buf, which is owned by

 *	the current task.  @buf->mutex must be locked.

 */

static void tty_audit_buf_push_current(struct tty_audit_buf *buf)

{

	tty_audit_buf_push(current, audit_get_loginuid(current->audit_context),

			   buf);

}



/**

 *	tty_audit_exit	-	Handle a task exit

 *

 *	Make sure all buffered data is written out and deallocate the buffer.

 *	Only needs to be called if current->signal->tty_audit_buf != %NULL.

 */

void tty_audit_exit(void)

{

	struct tty_audit_buf *buf;



	spin_lock_irq(&current->sighand->siglock);

	buf = current->signal->tty_audit_buf;

	current->signal->tty_audit_buf = NULL;

	spin_unlock_irq(&current->sighand->siglock);

	if (!buf)

		return;



	mutex_lock(&buf->mutex);

	tty_audit_buf_push_current(buf);

	mutex_unlock(&buf->mutex);



	tty_audit_buf_put(buf);

}



/**

 *	tty_audit_fork	-	Copy TTY audit state for a new task

 *

 *	Set up TTY audit state in @sig from current.  @sig needs no locking.

 */

void tty_audit_fork(struct signal_struct *sig)

{

	spin_lock_irq(&current->sighand->siglock);

	sig->audit_tty = current->signal->audit_tty;

	spin_unlock_irq(&current->sighand->siglock);

	sig->tty_audit_buf = NULL;

}



/**

 *	tty_audit_push_task	-	Flush task's pending audit data

 */

void tty_audit_push_task(struct task_struct *tsk, uid_t loginuid)

{

	struct tty_audit_buf *buf;



	spin_lock_irq(&tsk->sighand->siglock);

	buf = tsk->signal->tty_audit_buf;

	if (buf)

		atomic_inc(&buf->count);

	spin_unlock_irq(&tsk->sighand->siglock);

	if (!buf)

		return;



	mutex_lock(&buf->mutex);

	tty_audit_buf_push(tsk, loginuid, buf);

	mutex_unlock(&buf->mutex);



	tty_audit_buf_put(buf);

}



/**

 *	tty_audit_buf_get	-	Get an audit buffer.

 *

 *	Get an audit buffer for @tty, allocate it if necessary.  Return %NULL

 *	if TTY auditing is disabled or out of memory.  Otherwise, return a new

 *	reference to the buffer.

 */

static struct tty_audit_buf *tty_audit_buf_get(struct tty_struct *tty)

{

	struct tty_audit_buf *buf, *buf2;



	buf = NULL;

	buf2 = NULL;

	spin_lock_irq(&current->sighand->siglock);

	if (likely(!current->signal->audit_tty))

		goto out;

	buf = current->signal->tty_audit_buf;

	if (buf) {

		atomic_inc(&buf->count);

		goto out;

	}

	spin_unlock_irq(&current->sighand->siglock);



	buf2 = tty_audit_buf_alloc(tty->driver->major,

				   tty->driver->minor_start + tty->index,

				   tty->icanon);

	if (buf2 == NULL) {

		audit_log_lost("out of memory in TTY auditing");

		return NULL;

	}



	spin_lock_irq(&current->sighand->siglock);

	if (!current->signal->audit_tty)

		goto out;

	buf = current->signal->tty_audit_buf;

	if (!buf) {

		current->signal->tty_audit_buf = buf2;

		buf = buf2;

		buf2 = NULL;

	}

	atomic_inc(&buf->count);

	/* Fall through */

 out:

	spin_unlock_irq(&current->sighand->siglock);

	if (buf2)

		tty_audit_buf_free(buf2);

	return buf;

}



/**

 *	tty_audit_add_data	-	Add data for TTY auditing.

 *

 *	Audit @data of @size from @tty, if necessary.

 */

void tty_audit_add_data(struct tty_struct *tty, unsigned char *data,

			size_t size)

{

	struct tty_audit_buf *buf;

	int major, minor;



	if (unlikely(size == 0))

		return;



	buf = tty_audit_buf_get(tty);

	if (!buf)

		return;



	mutex_lock(&buf->mutex);

	major = tty->driver->major;

	minor = tty->driver->minor_start + tty->index;

	if (buf->major != major || buf->minor != minor

	    || buf->icanon != tty->icanon) {

		tty_audit_buf_push_current(buf);

		buf->major = major;

		buf->minor = minor;

		buf->icanon = tty->icanon;

	}

	do {

		size_t run;



		run = N_TTY_BUF_SIZE - buf->valid;

		if (run > size)

			run = size;

		memcpy(buf->data + buf->valid, data, run);

		buf->valid += run;

		data += run;

		size -= run;

		if (buf->valid == N_TTY_BUF_SIZE)

			tty_audit_buf_push_current(buf);

	} while (size != 0);

	mutex_unlock(&buf->mutex);

	tty_audit_buf_put(buf);

}



/**

 *	tty_audit_push	-	Push buffered data out

 *

 *	Make sure no audit data is pending for @tty on the current process.

 */

void tty_audit_push(struct tty_struct *tty)

{

	struct tty_audit_buf *buf;



	spin_lock_irq(&current->sighand->siglock);

	if (likely(!current->signal->audit_tty)) {

		spin_unlock_irq(&current->sighand->siglock);

		return;

	}

	buf = current->signal->tty_audit_buf;

	if (buf)

		atomic_inc(&buf->count);

	spin_unlock_irq(&current->sighand->siglock);



	if (buf) {

		int major, minor;



		major = tty->driver->major;

		minor = tty->driver->minor_start + tty->index;

		mutex_lock(&buf->mutex);

		if (buf->major == major && buf->minor == minor)

			tty_audit_buf_push_current(buf);

		mutex_unlock(&buf->mutex);

		tty_audit_buf_put(buf);

	}

}



/**

 *	tty_audit_opening	-	A TTY is being opened.

 *

 *	As a special hack, tasks that close all their TTYs and open new ones

 *	are assumed to be system daemons (e.g. getty) and auditing is

 *	automatically disabled for them.

 */

void tty_audit_opening(void)

{

	int disable;



	disable = 1;

	spin_lock_irq(&current->sighand->siglock);

	if (current->signal->audit_tty == 0)

		disable = 0;

	spin_unlock_irq(&current->sighand->siglock);

	if (!disable)

		return;



	task_lock(current);

	if (current->files) {

		struct fdtable *fdt;

		unsigned i;



		/*

		 * We don't take a ref to the file, so we must hold ->file_lock

		 * instead.

		 */

		spin_lock(&current->files->file_lock);

		fdt = files_fdtable(current->files);

		for (i = 0; i < fdt->max_fds; i++) {

			struct file *filp;



			filp = fcheck_files(current->files, i);

			if (filp && is_tty(filp)) {

				disable = 0;

				break;

			}

		}

		spin_unlock(&current->files->file_lock);

	}

	task_unlock(current);

	if (!disable)

		return;



	spin_lock_irq(&current->sighand->siglock);

	current->signal->audit_tty = 0;

	spin_unlock_irq(&current->sighand->siglock);

}

drivers/char/tty_io.c

+13 −1
Original line number Diff line number Diff line
@@ -1503,6 +1503,15 @@ int tty_hung_up_p(struct file * filp) 


EXPORT_SYMBOL(tty_hung_up_p);



/**

 * is_tty	-	checker whether file is a TTY

 */

int is_tty(struct file *filp)

{

	return filp->f_op->read == tty_read

		|| filp->f_op->read == hung_up_tty_read;

}



static void session_clear_tty(struct pid *session)

{

	struct task_struct *p;
@@ -2673,6 +2682,7 @@ got_driver: 
		__proc_set_tty(current, tty);

	spin_unlock_irq(&current->sighand->siglock);

	mutex_unlock(&tty_mutex);

	tty_audit_opening();

	return 0;

}
@@ -2735,8 +2745,10 @@ static int ptmx_open(struct inode * inode, struct file * filp) 


	check_tty_count(tty, "tty_open");

	retval = ptm_driver->open(tty, filp);

	if (!retval)

	if (!retval) {

		tty_audit_opening();

		return 0;

	}

out1:

	release_dev(filp);

	return retval;

include/linux/audit.h

+11 −0
Original line number Diff line number Diff line
@@ -63,9 +63,12 @@ 
#define AUDIT_ADD_RULE		1011	/* Add syscall filtering rule */

#define AUDIT_DEL_RULE		1012	/* Delete syscall filtering rule */

#define AUDIT_LIST_RULES	1013	/* List syscall filtering rules */

#define AUDIT_TTY_GET		1014	/* Get TTY auditing status */

#define AUDIT_TTY_SET		1015	/* Set TTY auditing status */



#define AUDIT_FIRST_USER_MSG	1100	/* Userspace messages mostly uninteresting to kernel */

#define AUDIT_USER_AVC		1107	/* We filter this differently */

#define AUDIT_USER_TTY		1124	/* Non-ICANON TTY input meaning */

#define AUDIT_LAST_USER_MSG	1199

#define AUDIT_FIRST_USER_MSG2	2100	/* More user space messages */

#define AUDIT_LAST_USER_MSG2	2999
@@ -92,6 +95,7 @@ 
#define AUDIT_KERNEL_OTHER	1316	/* For use by 3rd party modules */

#define AUDIT_FD_PAIR		1317    /* audit record for pipe/socketpair */

#define AUDIT_OBJ_PID		1318	/* ptrace target */

#define AUDIT_TTY		1319	/* Input on an administrative TTY */



#define AUDIT_AVC		1400	/* SE Linux avc denial or grant */

#define AUDIT_SELINUX_ERR	1401	/* Internal SE Linux Errors */
@@ -289,6 +293,10 @@ struct audit_status { 
	__u32		backlog;	/* messages waiting in queue */

};



struct audit_tty_status {

	__u32		enabled; /* 1 = enabled, 0 = disabled */

};



/* audit_rule_data supports filter rules with both integer and string

 * fields.  It corresponds with AUDIT_ADD_RULE, AUDIT_DEL_RULE and

 * AUDIT_LIST_RULES requests.
@@ -515,11 +523,13 @@ extern void audit_log_d_path(struct audit_buffer *ab, 
					     const char *prefix,

					     struct dentry *dentry,

					     struct vfsmount *vfsmnt);

extern void		    audit_log_lost(const char *message);

				/* Private API (for audit.c only) */

extern int audit_filter_user(struct netlink_skb_parms *cb, int type);

extern int audit_filter_type(int type);

extern int  audit_receive_filter(int type, int pid, int uid, int seq,

			 void *data, size_t datasz, uid_t loginuid, u32 sid);

extern int audit_enabled;

#else

#define audit_log(c,g,t,f,...) do { ; } while (0)

#define audit_log_start(c,g,t) ({ NULL; })
@@ -530,6 +540,7 @@ extern int audit_receive_filter(int type, int pid, int uid, int seq, 
#define audit_log_untrustedstring(a,s) do { ; } while (0)

#define audit_log_n_untrustedstring(a,n,s) do { ; } while (0)

#define audit_log_d_path(b,p,d,v) do { ; } while (0)

#define audit_enabled 0

#endif

#endif

#endif