On Fri, May 12, 2017 at 05:47:55PM -0400, Rik van Riel wrote: > > Seriously, look at these beasts. Overwriting ->addr_limit is nowhere > > near > > the top threat. If attacker can overwrite thread_info, you have > > lost. > > That is why THREAD_INFO_IN_TASK exists. It moves > the struct thread_info to a location away from the > stack, which means a stack overflow will not overwrite > the thread_info. ... in which case such attacks on ->addr_limit also become a non-issue. AFAICS, we are mixing several unrelated issues here: * amount of places where set_fs() is called. Sure, reducing it is a good idea and we want to move to primitives like kernel_write() et.al. Fewer users => lower odds of screwing it up. * making sure that remaining callers are properly paired. Ditto. * switching to ->read_iter()/->write_iter() where it makes sense. Again, no problem with that. * providing sane environment for places like perf/oprofile. Again, a good idea, and set_fs(USER_DS) is only a part of what's needed there. * switching _everything_ to ->read_iter()/->write_iter(). Flat-out insane and AFAICS nobody is signing up for that. * getting rid of set_fs() entirely. I'm afraid that it's not feasible without the previous one and frankly, I don't see much point. * sanity-checking on return to userland. Maybe useful, maybe not. * taking thread_info out of the way of stack overflows. Reasonable, but has very little to do with the rest of that. * protecting against Lovecraftian horrors slithering in from the outer space only to commit unspeakable acts against ->addr_limit and ignoring much tastier targets next to it, but then what do you expect from degenerate spawn of Great Old Ones - sanity? -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
