Kenton Varda <kenton@xxxxxxxxxxxx> writes: > On Thu, May 28, 2015 at 1:06 PM, Alexander Larsson <alexl@xxxxxxxxxx> wrote: >> On Thu, 2015-05-28 at 12:14 -0500, Eric W. Biederman wrote: >>> >>> > Where does the second namespace enter into this? >>> >>> Step a. Create create a user namespace where uid 0 is mapped to your >>> real uid, and set up your sandbox (aka mount /dev/pts and everything >>> else). >>> >>> Step b. Create a nested user namespace where your uid is identity >>> mapped and run your desktop application. You can even drop all caps >>> in >>> your namespace. >> >> Just tried this. Its not the nicest, and it doubles the number of >> namespaces in action for each sandbox, but it does work. > > How much overhead is involved in each user namespace? sizeof(struct user_namespace). > Is there any system-wide limit on total namespaces, other than RAM? There is a system-wide maximum depth, but not count. > Is there > (non-negligible) CPU overhead for each syscall seeking permissions in > the namespace? ns_capable(ns, X) in some cases can walk up the from a starting user namespace to the initial user. (The only non-constant operation I am aware of). However unless the user namespace depth is deep it should still take a negligible amount of time. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
