[PATCH V4] audit: add tty field to LOGIN event
Peter Hurley
peter at hurleysoftware.com
Thu Apr 28 19:32:05 UTC 2016
On 04/28/2016 12:28 PM, Richard Guy Briggs wrote:
> On 16/04/27, Peter Hurley wrote:
>> On 04/27/2016 06:31 PM, Richard Guy Briggs wrote:
>>> On 16/04/22, Peter Hurley wrote:
>>>> On 04/21/2016 11:14 AM, 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(). Lock and bump the kref to protect it, adding
>>>>> audit_put_tty() alias to decrement it.
>>>>>
>>>>> Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
>>>>> ---
>>>>>
>>>>> V4: Add missing prototype for audit_put_tty() when audit syscall is not
>>>>> enabled (MIPS).
>>>>>
>>>>> V3: Introduce audit_put_tty() alias to decrement kref.
>>>>>
>>>>> V2: Use kref to protect tty signal struct while in use.
>>>>>
>>>>> ---
>>>>>
>>>>> include/linux/audit.h | 24 ++++++++++++++++++++++++
>>>>> kernel/audit.c | 18 +++++-------------
>>>>> kernel/auditsc.c | 8 ++++++--
>>>>> 3 files changed, 35 insertions(+), 15 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/audit.h b/include/linux/audit.h
>>>>> index b40ed5d..32cdafb 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 +344,23 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
>>>>> return tsk->sessionid;
>>>>> }
>>>>>
>>>>> +static inline struct tty_struct *audit_get_tty(struct task_struct *tsk)
>>>>> +{
>>>>> + struct tty_struct *tty = NULL;
>>>>> + unsigned long flags;
>>>>> +
>>>>> + spin_lock_irqsave(&tsk->sighand->siglock, flags);
>>>>> + if (tsk->signal)
>>>>> + tty = tty_kref_get(tsk->signal->tty);
>>>>> + spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
>>>>
>>>>
>>>> Not that I'm objecting because I get that you're just refactoring
>>>> existing code, but I thought I'd point out some stuff.
>>>>
>>>> 1. There's no need to check if signal_struct is NULL (ie. tsk->signal)
>>>> because if it is, this will blow up trying to dereference the
>>>> sighand_struct (ie tsk->sighand).
>>>
>>> Ok. This logic goes back 10 years and one month less two days. (45d9bb0e)
>>>
>>>> 2. The existing usage is always tsk==current
>>>
>>> My understanding is that when it is called via:
>>>
>>> copy_process()
>>> audit_free()
>>> __audit_free()
>>> audit_log_exit()
>>> audit_log_task_info()
>>>
>>> then tsk != current.
>>
>> While it's true that tsk != current here, everything relevant to tty
>> in task_struct is the same because the nascent task is not even half-done.
>> So tsk->sighand == current->sighand, tsk->signal == current->signal etc.
>
> I agree this is true except in the case of !CLONE_SIGHAND, if it fails
> after copy_sighand() or copy_signal() then it would be null and would
> get freed before audit_free() is called. By the time tty gets copied
> from current in this case, it is past the point of failure in
> copy_process().
Oh, right.
>> If you're uncomfortable with pass-through execution like that, then the
>> simple solution is:
>>
>> struct tty_struct *tty = NULL;
>>
>> /* tsk != current when copy_process() failed */
>> if (tsk == current)
>> tty = get_current_tty();
>>
>> because tty_kref_put(tty) accepts NULL tty and (obviously) so does
>> tty_name(tty).
>
> Given the circumstances above, this appears reasonable to me at first
> look.
Ok.
I'll spend more analysis time before I actually submit a patch for this.
>>> This appears to be the only case which appears to
>>> force lugging around tsk. This is noted in that commit referenced
>>> above.
>>>
>>>> 3. If the idea is to make this invulnerable to tsk being gone, then
>>>> the usage is unsafe anyway.
>>>>
>>>>
>>>> So ultimately (but not necessarily for this patch) I'd prefer that either
>>>> a. audit use existing tty api instead of open-coding, or
>>>> b. add any tty api functions required.
>>>
>>> This latter option did cross my mind...
>>>
>>>> Peter Hurley
>>>>
>>>>> + return tty;
>>>>> +}
>>>>> +
>>>>> +static inline void audit_put_tty(struct tty_struct *tty)
>>>>> +{
>>>>> + tty_kref_put(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 +518,12 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
>>>>> {
>>>>> return -1;
>>>>> }
>>>>> +static inline struct tty_struct *audit_get_tty(struct task_struct *tsk)
>>>>> +{
>>>>> + return NULL;
>>>>> +}
>>>>> +static inline void audit_put_tty(struct tty_struct *tty)
>>>>> +{ }
>>>>> 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..7edd776 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>
>>>>>
>>>>> @@ -1873,21 +1872,14 @@ 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;
>>>>>
>>>>> /* 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 = audit_get_tty(tsk);
>>>>> audit_log_format(ab,
>>>>> " ppid=%d pid=%d auid=%u uid=%u gid=%u"
>>>>> " euid=%u suid=%u fsuid=%u"
>>>>> @@ -1903,11 +1895,11 @@ 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));
>>>>> -
>>>>> + tty ? tty_name(tty) : "(none)",
>>>>> + audit_get_sessionid(tsk));
>>>>> + audit_put_tty(tty);
>>>>> audit_log_format(ab, " comm=");
>>>>> audit_log_untrustedstring(ab, get_task_comm(comm, tsk));
>>>>> -
>>>>> audit_log_d_path_exe(ab, tsk->mm);
>>>>> audit_log_task_context(ab);
>>>>> }
>>>>> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
>>>>> index 195ffae..71e14d8 100644
>>>>> --- a/kernel/auditsc.c
>>>>> +++ b/kernel/auditsc.c
>>>>> @@ -1980,6 +1980,7 @@ static void audit_log_set_loginuid(kuid_t koldloginuid, kuid_t kloginuid,
>>>>> {
>>>>> struct audit_buffer *ab;
>>>>> uid_t uid, oldloginuid, loginuid;
>>>>> + struct tty_struct *tty;
>>>>>
>>>>> if (!audit_enabled)
>>>>> return;
>>>>> @@ -1987,14 +1988,17 @@ static void audit_log_set_loginuid(kuid_t koldloginuid, kuid_t kloginuid,
>>>>> uid = from_kuid(&init_user_ns, task_uid(current));
>>>>> oldloginuid = from_kuid(&init_user_ns, koldloginuid);
>>>>> loginuid = from_kuid(&init_user_ns, kloginuid),
>>>>> + tty = audit_get_tty(current);
>>>>>
>>>>> ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_LOGIN);
>>>>> if (!ab)
>>>>> 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);
>>>>> + audit_log_format(ab, " old-auid=%u auid=%u tty=%s old-ses=%u ses=%u res=%d",
>>>>> + oldloginuid, loginuid, tty ? tty_name(tty) : "(none)",
>>>>> + oldsessionid, sessionid, !rc);
>>>>> + audit_put_tty(tty);
>>>>> audit_log_end(ab);
>>>>> }
>>>>>
>>>>>
>>>>
>>>
>>> - RGB
>>>
>>> --
>>> Richard Guy Briggs <rgb at redhat.com>
>>> Kernel Security Engineering, Base Operating Systems, Red Hat
>>> Remote, Ottawa, Canada
>>> Voice: +1.647.777.2635, Internal: (81) 32635
>>>
>>
>
> - RGB
>
> --
> Richard Guy Briggs <rgb at redhat.com>
> Kernel Security Engineering, Base Operating Systems, Red Hat
> Remote, Ottawa, Canada
> Voice: +1.647.777.2635, Internal: (81) 32635
>
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