Re: [PATCH v12 07/13] seccomp: add SECCOMP_RET_ERRNO

[Serge Hallyn]

----- Original message -----
> On Fri, Mar 2, 2012 at 12:24 PM, Serge E. Hallyn <serge@xxxxxxxxxx>
> wrote:
> > Quoting Will Drewry (wad@xxxxxxxxxxxx):
> > > This change adds the SECCOMP_RET_ERRNO as a valid return value from a
> > > seccomp filter. ÂAdditionally, it makes the first use of the lower
> > > 16-bits for storing a filter-supplied errno. Â16-bits is more than
> > > enough for the errno-base.h calls.
> > > 
> > > Returning errors instead of immediately terminating processes that
> > > violate seccomp policy allow for broader use of this functionality
> > > for kernel attack surface reduction. ÂFor example, a linux container
> > > could maintain a whitelist of pre-existing system calls but drop
> > > all new ones with errnos. ÂThis would keep a logically static attack
> > > surface while providing errnos that may allow for graceful failure
> > > without the downside of do_exit() on a bad call.
> > > 
> > > v12: - move to WARN_ON if filter is NULL
> > > Â Â Â Â(oleg@xxxxxxxxxx, luto@xxxxxxx, keescook@xxxxxxxxxxxx)
> > > Â Â Â- return immediately for filter==NULL (keescook@xxxxxxxxxxxx)
> > > Â Â Â- change evaluation to only compare the ACTION so that layered
> > > Â Â Â Âerrnos don't result in the lowest one being returned.
> > > Â Â Â Â(keeschook@xxxxxxxxxxxx)
> > > v11: - check for NULL filter (keescook@xxxxxxxxxxxx)
> > > v10: - change loaders to fn
> > > Âv9: - n/a
> > > Âv8: - update Kconfig to note new need for syscall_set_return_value.
> > > Â Â Â- reordered such that TRAP behavior follows on later.
> > > Â Â Â- made the for loop a little less indent-y
> > > Âv7: - introduced
> > > 
> > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > > Signed-off-by: Will Drewry <wad@xxxxxxxxxxxx>
> > 
> > Clever :)
> > 
> > Thanks, Will.
> > 
> > For patches 1-7,
> > 
> > Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
> 
> Thanks!
> 
> > The -1 return value from __secure_computing_int() seems like it
> > could stand Â#define, like
> > 
> > #define SECCOMP_DONTRUN -1
> > #define SECCOMP_RUN 0
> > 
> > or something Maybe not, but -1 always scares me and I had to look back
> > and forth a few times to make sure it was doing what I would want.
> 
> Works for me.  The -1 just matches what syscall emulation, etc does on
> x86.  I'll add this to the tweaks for v14.
> 
> Thanks!

Well, in that case maybe it's not worth it.  Sounds
like ignorance on my part.

thanks,
-serge
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