Messages in this thread | | | Subject | Re: [PATCH] procfs: change the owner of non-dumpable and writeable files | From | Aleksa Sarai <> | Date | Thu, 19 Jan 2017 10:34:02 +1100 |
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>> In order to protect against ptrace(2) and similar attacks on container >> runtimes when they join namespaces, many runtimes set mm->dumpable to >> SUID_DUMP_DISABLE. However, doing this means that attempting to set up >> an unprivileged user namespace will fail because an unprivileged process >> can no longer access /proc/self/{setgroups,{uid,gid}_map} for the >> container process (which is the same uid as the runtime process). >> >> Fix this by changing pid_getattr to *also* change the owner of regular >> files that have a mode of 0644 (when the process is not dumpable). This >> ensures that the important /proc/[pid]/... files mentioned above are >> properly accessible by a container runtime in a rootless container >> context. >> >> The most blantant issue is that a non-dumpable process in a rootless >> container context is unable to open /proc/self/setgroups, because it >> doesn't own the file. > > This changes a lot more than just setgroups, doesn't it? This bypasses > the task_dumpable check for all kinds of things.
Yeah. I can special case /proc/self/setgroups as well as uid_map, gid_map and the other *specific* things that runC needs. But ultimately I think we should come up with agreement on what things should always appear to be owned by the process's user.
> Though, I expect the > has_pid_permissions() check to be the harder one to pass. Why does > has_pid_permissions() succeed in the case you've given?
Because the group id of the container process is the same as the parent process, so is_group_p() will succeed. Also hide_pid_min is set such that it will work in either case.
-- Aleksa Sarai Software Engineer (Containers) SUSE Linux GmbH https://www.cyphar.com/
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