On Fri, Aug 26, 2016 at 12:30:04PM -0400, robert.foss@xxxxxxxxxxxxx wrote: > From: Will Drewry <wad@xxxxxxxxxxxx> > > This patch proposes a sysctl knob that allows a privileged user to > disable ~VM_MAYEXEC tainting when mapping in a vma from a MNT_NOEXEC > mountpoint. It does not alter the normal behavior resulting from > attempting to directly mmap(PROT_EXEC) a vma (-EPERM) nor the behavior > of any other subsystems checking MNT_NOEXEC. Wouldn't it be equal to remounting all filesystems without noexec from attacker POV? It's hardly a fence to make additional mprotect(PROT_EXEC) call, before starting executing code from such filesystems. If administrator of the system wants this, he can just mount filesystem without noexec, no new kernel code required. And it's more fine-grained than this. So, no, I don't think we should add knob like this. Unless I miss something. NAK. > It is motivated by a common /dev/shm, /tmp usecase. There are few > facilities for creating a shared memory segment that can be remapped in > the same process address space with different permissions. What about using memfd_create(2) for such cases? You'll get a file descriptor from in-kernel tmpfs (shm_mnt) which is not exposed to userspace for remount as noexec. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>