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: Miloslav 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/include/linux/tty.h b/include/linux/tty.h
index deaba9ec5004..691a1748d9d2 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -178,6 +178,7 @@ struct tty_bufhead {
 #define L_IEXTEN(tty)   _L_FLAG((tty),IEXTEN)
 
 struct device;
+struct signal_struct;
 /*
  * Where all of the state associated with a tty is kept while the tty
  * is open.  Since the termios state should be kept even if the tty
@@ -310,6 +311,7 @@ extern void tty_hangup(struct tty_struct * tty);
 extern void tty_vhangup(struct tty_struct * tty);
 extern void tty_unhangup(struct file *filp);
 extern int tty_hung_up_p(struct file * filp);
+extern int is_tty(struct file *filp);
 extern void do_SAK(struct tty_struct *tty);
 extern void __do_SAK(struct tty_struct *tty);
 extern void disassociate_ctty(int priv);
@@ -347,6 +349,37 @@ extern int tty_write_lock(struct tty_struct *tty, int ndelay);
 /* n_tty.c */
 extern struct tty_ldisc tty_ldisc_N_TTY;
 
+/* tty_audit.c */
+#ifdef CONFIG_AUDIT
+extern void tty_audit_add_data(struct tty_struct *tty, unsigned char *data,
+                               size_t size);
+extern void tty_audit_exit(void);
+extern void tty_audit_fork(struct signal_struct *sig);
+extern void tty_audit_push(struct tty_struct *tty);
+extern void tty_audit_push_task(struct task_struct *tsk, uid_t loginuid);
+extern void tty_audit_opening(void);
+#else
+static inline void tty_audit_add_data(struct tty_struct *tty,
+                                      unsigned char *data, size_t size)
+{
+}
+static inline void tty_audit_exit(void)
+{
+}
+static inline void tty_audit_fork(struct signal_struct *sig)
+{
+}
+static inline void tty_audit_push(struct tty_struct *tty)
+{
+}
+static inline void tty_audit_push_task(struct task_struct *tsk, uid_t loginuid)
+{
+}
+static inline void tty_audit_opening(void)
+{
+}
+#endif
+
 /* tty_ioctl.c */
 extern int n_tty_ioctl(struct tty_struct * tty, struct file * file,
                        unsigned int cmd, unsigned long arg);