On Fri, May 12, 2017 at 2:06 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Fri, May 12, 2017 at 09:21:06PM +0100, Russell King - ARM Linux wrote: >> On Fri, May 12, 2017 at 12:30:02PM -0700, Kees Cook wrote: >> > I'm clearly not explaining things well enough. I shouldn't say >> > "corruption", I should say "malicious manipulation". The methodology >> > of attacks against the stack are quite different from the other kinds >> > of attacks like use-after-free, heap overflow, etc. Being able to >> > exhaust the kernel stack (either due to deep recursion or unbounded >> > alloca()) >> >> I really hope we don't have alloca() use in the kernel. Do you have >> evidence to support that assertion? >> >> IMHO alloca() (or similar) should not be present in any kernel code >> because we have a limited stack - we have kmalloc() etc for that kind >> of thing. > > No alloca(), but there are VLAs. Said that, the whole "what if they > can bugger thread_info and/or task_struct and go after set_fs() state" > is idiocy, of course - in that case the box is fucked, no matter what. Two things are at risk from stack exhaustion: thread_info (mainly addr_limit) when on the stack (fixed by THREAD_INFO_IN_TASK), and overflow into adjacent allocations (fixed by VMAP_STACK). The latter is fundamentally a heap overflow. -Kees -- Kees Cook Pixel Security -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
