I've been in communication with the upstream namespace maintainer, and the intention was certainly that what you're doing should fail. However there was an oversight that missed the O_CREAT case. Due to some differences in 4.4 the backport did cover that case.
As I mentioned above, you can still do what your trying to do, you just need to make sure your process's fsuid/fsgid are mapped into the containers user namespace before creating the file. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1659087 Title: open(2) returns EOVERFLOW within tmpfs+userns Status in linux package in Ubuntu: Confirmed Status in linux source package in Xenial: Confirmed Bug description: On Ubuntu 4.4.0-59.80-generic 4.4.35, open(2) returns EOVERFLOW when creating a file in tmpfs with user namespace enabled. This issue wasn't present in 4.4.0-47 and has probably been introduced by https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1634964 Step to reproduce: $ unshare -r -U -m /bin/bash # mount -t tmpfs tmpfs /mnt # echo $$ 2354 In another terminal: $ sudo nsenter -t 2354 -m # touch /mnt/foo touch: cannot touch '/mnt/foo': Value too large for defined data type Note that we are not joining the user namespace when creating the file but we would expect `touch' to succeed and create the file with an inode set to INVALID_UID/GID (i.e. nobody:nogroup) within the mount namespace. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1659087/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
