On Wed, Jan 13, 2021 at 6:22 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > 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. I'll do my best but I'm also not a security expert. Will post the next version with a draft for the man page (this syscall does not have a man page yet AFAIKT) and we can iterate on the wording there. > > 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. Great. SOunds like the only missing piece is the man page with more details. I'll work on it but since it's the first time I will be contributing to man pages it might take me a couple days. Thanks everyone for the reviews! > -- > Michal Hocko > SUSE Labs
