On Tue 12-01-21 09:51:24, Suren Baghdasaryan wrote: > On Tue, Jan 12, 2021 at 9:45 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > > On 01/12, Michal Hocko wrote: > > > > > > On Mon 11-01-21 09:06:22, Suren Baghdasaryan wrote: > > > > > > > What we want is the ability for one process to influence another process > > > > in order to optimize performance across the entire system while leaving > > > > the security boundary intact. > > > > Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ > > > > and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata > > > > and CAP_SYS_NICE for influencing process performance. > > > > > > I have to say that ptrace modes are rather obscure to me. So I cannot > > > really judge whether MODE_READ is sufficient. My understanding has > > > always been that this is requred to RO access to the address space. But > > > this operation clearly has a visible side effect. Do we have any actual > > > documentation for the existing modes? > > > > > > I would be really curious to hear from Jann and Oleg (now Cced). > > > > Can't comment, sorry. I never understood these security checks and never tried. > > IIUC only selinux/etc can treat ATTACH/READ differently and I have no idea what > > is the difference. > > I haven't seen a written explanation on ptrace modes but when I > consulted Jann his explanation was: > > PTRACE_MODE_READ means you can inspect metadata about processes with > the specified domain, across UID boundaries. > PTRACE_MODE_ATTACH means you can fully impersonate processes with the > specified domain, across UID boundaries. Maybe this would be a good start to document expectations. Some more practical examples where the difference is visible would be great as well. > He did agree that in this case PTRACE_MODE_ATTACH seems too > restrictive (we do not try to gain full control or impersonate a > process) and PTRACE_MODE_READ is a better choice. All that being said, I am not against the changed behavior but I do not feel competent to give an ack. -- Michal Hocko SUSE Labs
