Trying the fsuid/fsgid workaround, I came across another oddity: $ id -u 1000 $ id -g 1000 $ unshare -r -U -m /bin/bash # mount -t tmpfs tmpfs /mnt # chmod 555 /mnt # ls -ldn /mnt dr-xr-xr-x 2 0 0 40 Jan 26 14:15 /mnt # echo $$ 2354
In another terminal: $ sudo nsenter -G 1000 -S 1000 -t 2354 -m $ ls -ldn /mnt dr-xr-xr-x 2 1000 1000 40 Jan 26 14:10 /mnt $ touch /mnt/foo touch: cannot touch '/mnt/foo': Permission denied Even though I'm supposed to be root in the context of the user namespace, I can't create the file because I'm lacking the write permission on the mount directory. In this case, setting the fsuid/fsgid is not sufficient, I have to join the user namespace if I want the permissions to be resolved correctly. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1659087 Title: open(2) returns EOVERFLOW within tmpfs+userns Status in linux package in Ubuntu: Confirmed Status in linux source package in Xenial: Confirmed Bug description: On Ubuntu 4.4.0-59.80-generic 4.4.35, open(2) returns EOVERFLOW when creating a file in tmpfs with user namespace enabled. This issue wasn't present in 4.4.0-47 and has probably been introduced by https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1634964 Step to reproduce: $ unshare -r -U -m /bin/bash # mount -t tmpfs tmpfs /mnt # echo $$ 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
