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 -- 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
