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>

3 files changed, 48 insertions, 0 deletions

diff --git a/include/linux/audit.h b/include/linux/audit.h
index fccc6e5..8ca7ca0 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -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
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3cffc12..b579624 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -529,6 +529,10 @@ struct signal_struct {
 #ifdef CONFIG_TASKSTATS
 	struct taskstats *stats;
 #endif
+#ifdef CONFIG_AUDIT
+	unsigned audit_tty;
+	struct tty_audit_buf *tty_audit_buf;
+#endif
 };
 
 /* Context switch must be unlocked if interrupts are to be enabled */
diff --git a/include/linux/tty.h b/include/linux/tty.h
index deaba9e..691a174 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);