Re: [PATCH 2/2] seccomp: Audit SECCOMP_RET_ERRNO actions with errno values

[Steve Grubb <sgrubb@redhat.com>]

On Monday, January 2, 2017 5:42:47 PM EST Tyler Hicks wrote:
> 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@canonical.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?

Typically when the layout has to change, we just give it a new record type.

 -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. */