linux-kernel - Re: [PATCH] audit: add tty field to LOGIN event

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Date:	Wed, 13 Apr 2016 17:31:16 -0700
From:	Peter Hurley <peter@...leysoftware.com>
To:	Richard Guy Briggs <rgb@...hat.com>, linux-audit@...hat.com,
	linux-kernel@...r.kernel.org
Cc:	sgrubb@...hat.com, pmoore@...hat.com, eparis@...hat.com
Subject: Re: [PATCH] audit: add tty field to LOGIN event

Hi Richard,

On 04/13/2016 04:25 PM, Richard Guy Briggs wrote:
> The tty field was missing from AUDIT_LOGIN events.
> 
> Refactor code to create a new function audit_get_tty(), using it to
> replace the call in audit_log_task_info() and to add it to
> audit_log_set_loginuid().
> 
> Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> ---
>  include/linux/audit.h |   18 ++++++++++++++++++
>  kernel/audit.c        |   11 +----------
>  kernel/auditsc.c      |    5 +++--
>  3 files changed, 22 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index b40ed5d..20c6649 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -26,6 +26,7 @@
>  #include <linux/sched.h>
>  #include <linux/ptrace.h>
>  #include <uapi/linux/audit.h>
> +#include <linux/tty.h>
>  
>  #define AUDIT_INO_UNSET ((unsigned long)-1)
>  #define AUDIT_DEV_UNSET ((dev_t)-1)
> @@ -343,6 +344,19 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
>  	return tsk->sessionid;
>  }
>  
> +static inline char *audit_get_tty(struct task_struct *tsk)
> +{
> +	char *tty;
> +
> +	spin_lock_irq(&tsk->sighand->siglock);
> +	if (tsk->signal && tsk->signal->tty && tsk->signal->tty->name)
> +		tty = tsk->signal->tty->name;
> +	else
> +		tty = "(none)";
> +	spin_unlock_irq(&tsk->sighand->siglock);

This is unsafe because the tty could be immediately torn down after the
siglock is dropped, and return a dangling ptr.


> +	return tty;
> +}
> +
>  extern void __audit_ipc_obj(struct kern_ipc_perm *ipcp);
>  extern void __audit_ipc_set_perm(unsigned long qbytes, uid_t uid, gid_t gid, umode_t mode);
>  extern void __audit_bprm(struct linux_binprm *bprm);
> @@ -500,6 +514,10 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
>  {
>  	return -1;
>  }
> +static inline char *audit_get_tty(struct task_struct *tsk)
> +{
> +	return "(invalid)";
> +}
>  static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
>  { }
>  static inline void audit_ipc_set_perm(unsigned long qbytes, uid_t uid,
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 3a3e5de..fae11df 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -64,7 +64,6 @@
>  #include <linux/security.h>
>  #endif
>  #include <linux/freezer.h>
> -#include <linux/tty.h>
>  #include <linux/pid_namespace.h>
>  #include <net/netns/generic.h>
>  
> @@ -1873,7 +1872,6 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
>  {
>  	const struct cred *cred;
>  	char comm[sizeof(tsk->comm)];
> -	char *tty;

	struct tty_struct *tty;

>  
>  	if (!ab)
>  		return;
> @@ -1881,13 +1879,6 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
>  	/* tsk == current */
>  	cred = current_cred();
>  
> -	spin_lock_irq(&tsk->sighand->siglock);
> -	if (tsk->signal && tsk->signal->tty && tsk->signal->tty->name)
> -		tty = tsk->signal->tty->name;
> -	else
> -		tty = "(none)";
> -	spin_unlock_irq(&tsk->sighand->siglock);

	tty = get_current_tty();
	
> -
>  	audit_log_format(ab,
>  			 " ppid=%d pid=%d auid=%u uid=%u gid=%u"
>  			 " euid=%u suid=%u fsuid=%u"
> @@ -1903,7 +1894,7 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
>  			 from_kgid(&init_user_ns, cred->egid),
>  			 from_kgid(&init_user_ns, cred->sgid),
>  			 from_kgid(&init_user_ns, cred->fsgid),
> -			 tty, audit_get_sessionid(tsk));
> +			 audit_get_tty(tsk), audit_get_sessionid(tsk));

			tty_name(tty), ....);
			^^^^^^^^^^
			returns "NULL tty" if tty == NULL

	tty_kref_put(tty);


>  
>  	audit_log_format(ab, " comm=");
>  	audit_log_untrustedstring(ab, get_task_comm(comm, tsk));
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 195ffae..a0467fb 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -1993,8 +1993,9 @@ static void audit_log_set_loginuid(kuid_t koldloginuid, kuid_t kloginuid,
>  		return;
>  	audit_log_format(ab, "pid=%d uid=%u", task_pid_nr(current), uid);
>  	audit_log_task_context(ab);
> -	audit_log_format(ab, " old-auid=%u auid=%u old-ses=%u ses=%u res=%d",
> -			 oldloginuid, loginuid, oldsessionid, sessionid, !rc);

	tty = get_current_tty();

> +	audit_log_format(ab, " old-auid=%u auid=%u tty=%s old-ses=%u ses=%u res=%d",
> +			 oldloginuid, loginuid, audit_get_tty(current),

			......., tty_name(tty),

> +			 oldsessionid, sessionid, !rc);

	tty_kref_put(tty);

Regards,
Peter Hurley


>  	audit_log_end(ab);
>  }
>  
>