linux-kernel - Re: [PATCH 2/2] seccomp: Audit SECCOMP_RET

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Message-ID: <20170102174246.GA17677@sec>
Date:   Mon, 2 Jan 2017 17:42:47 +0000
From:   Tyler Hicks <tyhicks@...onical.com>
To:     Steve Grubb <sgrubb@...hat.com>
Cc:     linux-audit@...hat.com, Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] seccomp: Audit SECCOMP_RET_ERRNO actions with errno
 values

On 2017-01-02 12:20:53, Steve Grubb wrote:
> On Monday, January 2, 2017 4:53:10 PM EST Tyler Hicks wrote:
> > Generate audit records for SECCOMP_RET_ERRNO actions, which were
> > previously not audited.
> > 
> > Additionally, include the errno value that will be set in the audit
> > message.
> > 
> > Signed-off-by: Tyler Hicks <tyhicks@...onical.com>
> > ---
> >  include/linux/audit.h | 19 ++++++++++++++++++-
> >  kernel/auditsc.c      |  3 +++
> >  kernel/seccomp.c      |  4 +++-
> >  3 files changed, 24 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > index 8c588c3..6815812 100644
> > --- a/include/linux/audit.h
> > +++ b/include/linux/audit.h
> > @@ -87,7 +87,10 @@ struct audit_field {
> > 
> >  struct audit_seccomp_info {
> >  	int		code;
> > -	long		signr;
> > +	union {
> > +		int	errno;
> > +		long	signr;
> > +	};
> >  };
> > 
> >  extern int is_audit_feature_set(int which);
> > @@ -319,6 +322,20 @@ static inline void audit_inode_child(struct inode
> > *parent, }
> >  void audit_core_dumps(long signr);
> > 
> > +static inline void audit_seccomp_errno(unsigned long syscall, int errno,
> > +				       int code)
> > +{
> > +	if (!audit_enabled)
> > +		return;
> > +
> > +	if (errno || unlikely(!audit_dummy_context())) {
> > +		struct audit_seccomp_info info = { .code = code,
> > +						   .errno = errno };
> > +
> > +		__audit_seccomp(syscall, &info);
> > +	}
> > +}
> > +
> >  static inline void audit_seccomp_signal(unsigned long syscall, long signr,
> >  					int code)
> >  {
> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index b3472f2..db5fc9d 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -2426,6 +2426,9 @@ void __audit_seccomp(unsigned long syscall, struct
> > audit_seccomp_info *info) audit_log_task(ab);
> > 
> >  	switch (info->code) {
> > +	case SECCOMP_RET_ERRNO:
> > +		audit_log_format(ab, " errno=%d", info->errno);
> > +		break;
> 
> "exit" is the field name that syscalls use to return errno to user space. I'd
> rather not see another field created that maps to the same thing. You can check
> the translation with the auformat utility:

Thanks for having a look at the field name I was using. Although I
prefer "errno" over "exit" in terms of clarity, I agree that it makes
sense to be consistent with the field names across record types. "exit"
works for me.

> 
> http://people.redhat.com/sgrubb/files/auformat.tar.gz
> 
> $ ausearch --start today --just-one -m syscall -sv no --raw | ./auformat "%EXIT\n"
> 
> Also, I am working to normalize all the records. That mean every event record
> of the same type has the same fields, in the same order, with the same
> representation. I would think "exit" could be added to the current record after
> syscall so that its ordered similarly to a syscall record.

This patch goes against your normalization efforts in more ways than
just the placement of the "exit" field. If the action is
SECCOMP_RET_KILL, a "sig" field is present but if the action is
SECCOMP_RET_ERRNO, the "sig" field will not be present but the "errno"
field will be present. This happens all within the AUDIT_SECCOMP record
type. How would you suggest normalizing AUDIT_SECCOMP records for
different seccomp return actions?

Tyler

> 
> -Steve
> 
> >  	case SECCOMP_RET_KILL:
> >  		audit_log_format(ab, " sig=%ld", info->signr);
> >  		break;
> > diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> > index 54c01b6..e99c566 100644
> > --- a/kernel/seccomp.c
> > +++ b/kernel/seccomp.c
> > @@ -576,9 +576,11 @@ static int __seccomp_filter(int this_syscall, const
> > struct seccomp_data *sd, /* Set low-order bits as an errno, capped at
> > MAX_ERRNO. */
> >  		if (data > MAX_ERRNO)
> >  			data = MAX_ERRNO;
> > +
> > +		audit_seccomp_errno(this_syscall, data, action);
> >  		syscall_set_return_value(current, task_pt_regs(current),
> >  					 -data, 0);
> > -		goto skip;
> > +		return -1;
> > 
> >  	case SECCOMP_RET_TRAP:
> >  		/* Show the handler the original registers. */
> 
> 

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