On Wed, Feb 22, 2012 at 5:53 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > On Wed, Feb 22, 2012 at 3:38 PM, Andrew Lutomirski <luto@xxxxxxx> wrote: >> On Wed, Feb 22, 2012 at 11:48 AM, Will Drewry <wad@xxxxxxxxxxxx> wrote: >>> On Wed, Feb 22, 2012 at 2:34 AM, Indan Zupancic <indan@xxxxxx> wrote: >>>> On Tue, February 21, 2012 18:30, Will Drewry wrote: >>>>> This change enables SIGSYS, defines _sigfields._sigsys, and adds >>>>> x86 (compat) arch support. _sigsys defines fields which allow >>>>> a signal handler to receive the triggering system call number, >>>>> the relevant AUDIT_ARCH_* value for that number, and the address >>>>> of the callsite. >>>>> >>>>> To ensure that SIGSYS delivery occurs on return from the triggering >>>>> system call, SIGSYS is added to the SYNCHRONOUS_MASK macro. I'm >>>>> this is enough to ensure it will be synchronous or if it is explicitly >>>>> required to ensure an immediate delivery of the signal upon return from >>>>> the blocked system call. >>>>> >>>>> The first consumer of SIGSYS would be seccomp filter. In particular, >>>>> a filter program could specify a new return value, SECCOMP_RET_TRAP, >>>>> which would result in the system call being denied and the calling >>>>> thread signaled. This also means that implementing arch-specific >>>>> support can be dependent upon HAVE_ARCH_SECCOMP_FILTER. >>>> >>>> I think others said this is useful, but I don't see how. Easier >>>> debugging compared to checking return values? >>>> >>>> I suppose SIGSYS can be blocked, so there is no guarantee the process >>>> will be killed. >>> >>> Yeah, this allows for in-process system call emulation, if desired, or >>> for the process to dump core/etc. With RET_ERRNO or RET_KILL, there >>> isn't any feedback to the system about the state of the process. Kill >>> populates audit_seccomp and dmesg, but if the application >>> user/developer isn't the system admin, installing audit bits or >>> checking system logs seems onerous. >> >> [Warning: this suggestion may be bad for any number of reasons] >> >> I wonder if it would be helpful to change the semantics of RET_KILL >> slightly. Rather than killing via do_exit, what if it killed via a >> forcibly-fatal SIGSYS? That way, the parent's waitid() / SIGCHLD >> would indicate CLD_KILLED with si_status == SIGSYS. The parent could >> check that and report that the child was probably compromised. >> >> --Andy > > I'd prefer sticking with do_exit. This provides much less chance of > things going wrong. A parent seeing a child killed with SIGKILL is > already pretty distinct, IMO. Hrm, it might be possible to do_exit(SIGSYS) which would be both. It looks like tsk->exit_code would be SIGSYS then, but I'll look a little more closely to see what that'll actually do. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
