When upgrading from xenial kernel (4.4.0-145) to linux-image-generic-hwe-16.04 (4.15.0-47) I am no longer able to run an application that checks it's data directory for write access/path traversal when that directory is an NFS share. This works on 4.4 and 3.13 kernels that I tested with but fails on 4.15. I'm using NFSv3 and have seen the behavior with both a synology NAS as the nfs-server as well as my xenial desktop as the nfs-server.
To reproduce:
0.) Boot test machine with kernel 4.15.0-47
1.) set up a NFS export on another machine (nfs-server)
/etc/exports:
/srv/nfstest 192.168.100.100(rw,sync,no_subtree_check)
2.) mount the NFS share on the test machine and give a non-root user ownership of the mount, in my case I have a user: aptly, with home=/var/lib/aptly, and I mounted the NFS at /var/lib/aptly/test. aptly:aptly owns /var/lib/aptly/test.
/etc/fstab:
192.168.100.101:/srv/nfstest /var/lib/aptly/test nfs rw,mountvers=3
3.) attempt to call access.W_OK on the mount as the non-root user `strace ./testaccess.py`
stderr:
...
access("/var/lib/aptly/test", W_OK) = -1 EACCES (Permission denied)
...
stdout:
('Writeable:', False)
('user r,e,s', (5062, 5062, 5062))
('group r,e,s', (5062, 5062, 5062))
posix.stat_result(st_mode=16895, st_ino=101188113, st_dev=48, st_nlink=3, st_uid=5062, st_gid=5062, st_size=4096, st_atime=1554858490, st_mtime=1554858633, st_ctime=1554858633)
testaccess.py:
#!/usr/bin/python
import os
import sys
from pprint import pprint
directory = '/var/lib/aptly/test'
if __name__ == "__main__":
writeable = os.access(directory, os.W_OK)
print("Writeable:", writeable)
print("user r,e,s", os.getresuid())
print("group r,e,s", os.getresgid())
pprint(os.stat(directory))
---
AlsaDevices:
total 0
crw-rw---- 1 root audio 116, 1 Apr 9 18:53 seq
crw-rw---- 1 root audio 116, 33 Apr 9 18:53 timer
AplayDevices: Error: [Errno 2] No such file or directory
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
DistroRelease: Ubuntu 16.04
HibernationDevice: RESUME=/dev/mapper/pao03--aptly01--vg-swap_1
InstallationDate: Installed on 2019-04-09 (1 days ago)
InstallationMedia: Ubuntu-Server 16.04.5 LTS "Xenial Xerus" - Release amd64 (20180731)
IwConfig: Error: [Errno 2] No such file or directory
Lsusb: Error: command ['lsusb'] failed with exit code 1:
MachineType: VMware, Inc. VMware Virtual Platform
Package: linux (not installed)
PciMultimedia:
ProcFB: 0 svgadrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.15.0-47-generic root=/dev/mapper/pao03--aptly01--vg-root ro
ProcVersionSignature: Ubuntu 4.15.0-47.50~16.04.1-generic 4.15.18
RelatedPackageVersions:
linux-restricted-modules-4.15.0-47-generic N/A
linux-backports-modules-4.15.0-47-generic N/A
linux-firmware 1.157.21
RfKill: Error: [Errno 2] No such file or directory
Tags: xenial xenial
Uname: Linux 4.15.0-47-generic x86_64
UnreportableReason: The report belongs to a package that is not installed.
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:
_MarkForUpload: False
dmi.bios.date: 07/28/2017
dmi.bios.vendor: Phoenix Technologies LTD
dmi.bios.version: 6.00
dmi.board.name: 440BX Desktop Reference Platform
dmi.board.vendor: Intel Corporation
dmi.board.version: None
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 1
dmi.chassis.vendor: No Enclosure
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnPhoenixTechnologiesLTD:bvr6.00:bd07/28/2017:svnVMware,Inc.:pnVMwareVirtualPlatform:pvrNone:rvnIntelCorporation:rn440BXDesktopReferencePlatform:rvrNone:cvnNoEnclosure:ct1:cvrN/A:
dmi.product.name: VMware Virtual Platform
dmi.product.version: None
dmi.sys.vendor: VMware, Inc.
This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:
apport-collect 1824050
and then change the status of the bug to 'Confirmed'.
If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.
This change has been made by an automated script, maintained by the Ubuntu Kernel Team.