tty: audit: Handle tty audit enable atomically

The audit_tty and audit_tty_log_passwd fields are actually bool
values, so merge into single memory location to access atomically.

NB: audit log operations may still occur after tty audit is disabled
which is consistent with the existing functionality

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_audit.c b/drivers/tty/tty_audit.c
index 50380d8..3d90f88 100644 (file)
--- a/drivers/tty/tty_audit.c
+++ b/drivers/tty/tty_audit.c
@@ -131,7 +131,6 @@ void tty_audit_exit(void)
 void tty_audit_fork(struct signal_struct *sig)
 {
        sig->audit_tty = current->signal->audit_tty;
-       sig->audit_tty_log_passwd = current->signal->audit_tty_log_passwd;
 }
 
 /**
@@ -141,11 +140,9 @@ void tty_audit_tiocsti(struct tty_struct *tty, char ch)
 {
        struct tty_audit_buf *buf;
        dev_t dev;
-       int should_audit;
        unsigned long flags;
 
        spin_lock_irqsave(&current->sighand->siglock, flags);
-       should_audit = current->signal->audit_tty;
        buf = current->signal->tty_audit_buf;
        if (buf)
                atomic_inc(&buf->count);
@@ -160,7 +157,7 @@ void tty_audit_tiocsti(struct tty_struct *tty, char ch)
                tty_audit_buf_put(buf);
        }
 
-       if (should_audit && audit_enabled) {
+       if (audit_enabled && (current->signal->audit_tty & AUDIT_TTY_ENABLE)) {
                kuid_t auid;
                unsigned int sessionid;
 
@@ -177,29 +174,25 @@ void tty_audit_tiocsti(struct tty_struct *tty, char ch)
  */
 int tty_audit_push(void)
 {
-       struct tty_audit_buf *buf = ERR_PTR(-EPERM);
+       struct tty_audit_buf *buf;
        unsigned long flags;
 
+       if (~current->signal->audit_tty & AUDIT_TTY_ENABLE)
+               return -EPERM;
+
        spin_lock_irqsave(&current->sighand->siglock, flags);
-       if (current->signal->audit_tty) {
-               buf = current->signal->tty_audit_buf;
-               if (buf)
-                       atomic_inc(&buf->count);
-       }
+       buf = current->signal->tty_audit_buf;
+       if (buf)
+               atomic_inc(&buf->count);
        spin_unlock_irqrestore(&current->sighand->siglock, flags);
 
-       /*
-        * Return 0 when signal->audit_tty set
-        * but current->signal->tty_audit_buf == NULL.
-        */
-       if (!buf || IS_ERR(buf))
-               return PTR_ERR(buf);
-
-       mutex_lock(&buf->mutex);
-       tty_audit_buf_push(buf);
-       mutex_unlock(&buf->mutex);
+       if (buf) {
+               mutex_lock(&buf->mutex);
+               tty_audit_buf_push(buf);
+               mutex_unlock(&buf->mutex);
 
-       tty_audit_buf_put(buf);
+               tty_audit_buf_put(buf);
+       }
        return 0;
 }
 
@@ -218,8 +211,6 @@ static struct tty_audit_buf *tty_audit_buf_get(void)
        buf = NULL;
        buf2 = NULL;
        spin_lock_irqsave(&current->sighand->siglock, flags);
-       if (likely(!current->signal->audit_tty))
-               goto out;
        buf = current->signal->tty_audit_buf;
        if (buf) {
                atomic_inc(&buf->count);
@@ -233,9 +224,10 @@ static struct tty_audit_buf *tty_audit_buf_get(void)
                return NULL;
        }
 
-       spin_lock_irqsave(&current->sighand->siglock, flags);
-       if (!current->signal->audit_tty)
+       if (~current->signal->audit_tty & AUDIT_TTY_ENABLE)
                goto out;
+
+       spin_lock_irqsave(&current->sighand->siglock, flags);
        buf = current->signal->tty_audit_buf;
        if (!buf) {
                current->signal->tty_audit_buf = buf2;
@@ -259,9 +251,8 @@ static struct tty_audit_buf *tty_audit_buf_get(void)
 void tty_audit_add_data(struct tty_struct *tty, const void *data, size_t size)
 {
        struct tty_audit_buf *buf;
-       int audit_log_tty_passwd;
-       unsigned long flags;
        unsigned int icanon = !!L_ICANON(tty);
+       unsigned int audit_tty;
        dev_t dev;
 
        if (unlikely(size == 0))
@@ -271,10 +262,10 @@ void tty_audit_add_data(struct tty_struct *tty, const void *data, size_t size)
            && tty->driver->subtype == PTY_TYPE_MASTER)
                return;
 
-       spin_lock_irqsave(&current->sighand->siglock, flags);
-       audit_log_tty_passwd = current->signal->audit_tty_log_passwd;
-       spin_unlock_irqrestore(&current->sighand->siglock, flags);
-       if (!audit_log_tty_passwd && icanon && !L_ECHO(tty))
+       audit_tty = READ_ONCE(current->signal->audit_tty);
+       if (~audit_tty & AUDIT_TTY_ENABLE)
+               return;
+       if ((~audit_tty & AUDIT_TTY_LOG_PASSWD) && icanon && !L_ECHO(tty))
                return;
 
        buf = tty_audit_buf_get();

diff --git a/include/linux/audit.h b/include/linux/audit.h
index b40ed5d..e38e3fc 100644 (file)
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -109,6 +109,10 @@ extern int audit_classify_compat_syscall(int abi, unsigned syscall);
 /* maximized args number that audit_socketcall can process */
 #define AUDITSC_ARGS           6
 
+/* bit values for ->signal->audit_tty */
+#define AUDIT_TTY_ENABLE       BIT(0)
+#define AUDIT_TTY_LOG_PASSWD   BIT(1)
+
 struct filename;
 
 extern void audit_log_session_info(struct audit_buffer *ab);

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a10494a..a389222 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -775,7 +775,6 @@ struct signal_struct {
 #endif
 #ifdef CONFIG_AUDIT
        unsigned audit_tty;
-       unsigned audit_tty_log_passwd;
        struct tty_audit_buf *tty_audit_buf;
 #endif
 

diff --git a/kernel/audit.c b/kernel/audit.c
index 610f221..2651e42 100644 (file)
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1030,20 +1030,19 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
                break;
        case AUDIT_TTY_GET: {
                struct audit_tty_status s;
-               struct task_struct *tsk = current;
+               unsigned int t;
 
-               spin_lock(&tsk->sighand->siglock);
-               s.enabled = tsk->signal->audit_tty;
-               s.log_passwd = tsk->signal->audit_tty_log_passwd;
-               spin_unlock(&tsk->sighand->siglock);
+               t = READ_ONCE(current->signal->audit_tty);
+               s.enabled = t & AUDIT_TTY_ENABLE;
+               s.log_passwd = !!(t & AUDIT_TTY_LOG_PASSWD);
 
                audit_send_reply(skb, seq, AUDIT_TTY_GET, 0, 0, &s, sizeof(s));
                break;
        }
        case AUDIT_TTY_SET: {
                struct audit_tty_status s, old;
-               struct task_struct *tsk = current;
                struct audit_buffer     *ab;
+               unsigned int t;
 
                memset(&s, 0, sizeof(s));
                /* guard against past and future API changes */
@@ -1053,14 +1052,14 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
                    (s.log_passwd != 0 && s.log_passwd != 1))
                        err = -EINVAL;
 
-               spin_lock(&tsk->sighand->siglock);
-               old.enabled = tsk->signal->audit_tty;
-               old.log_passwd = tsk->signal->audit_tty_log_passwd;
-               if (!err) {
-                       tsk->signal->audit_tty = s.enabled;
-                       tsk->signal->audit_tty_log_passwd = s.log_passwd;
+               if (err)
+                       t = READ_ONCE(current->signal->audit_tty);
+               else {
+                       t = s.enabled | (-s.log_passwd & AUDIT_TTY_LOG_PASSWD);
+                       t = xchg(&current->signal->audit_tty, t);
                }
-               spin_unlock(&tsk->sighand->siglock);
+               old.enabled = t & AUDIT_TTY_ENABLE;
+               old.log_passwd = !!(t & AUDIT_TTY_LOG_PASSWD);
 
                audit_log_common_recv_msg(&ab, AUDIT_CONFIG_CHANGE);
                audit_log_format(ab, " op=tty_set old-enabled=%d new-enabled=%d"