shiftfs: broken shiftfs nesting

[Christian Brauner]

SRU Justification

Impact: When nested containers use shiftfs and they have different id mappings the nested container lacks privileges to create any files in its root filesystem unless the directory in question is very permissive. This prevents nested containers from being usable.
Here is a reproducer as given by Stéphane:

Reproducer:
 - lxc init images:ubuntu/bionic b1 -c security.nesting=true
 - Confirm b1 uses shiftfs and uses the default map

root@b1:~# cat /proc/self/uid_map
         0 1000000 1000000000
root@b1:~# grep shiftfs /proc/self/mountinfo
3702 2266 0:92 / / rw,relatime - shiftfs /var/lib/lxd/storage-pools/default/containers/b1/rootfs rw,passthrough=3

 - Install LXD snap in there
 - snap set lxd shiftfs.enable=true
 - systemctl reload snap.lxd.daemon
 - lxd init --auto
 - lxc launch images:alpine/edge a1
 - Confirm that a1 uses a different map than b1
 - Confirm that a1 uses shiftfs
 - touch /etc/a should fail with EACCES

Fix: Instead of recording the credentials of the process that created the innermost shiftfs mount we need to record the credentials of the lowers creator of the first shiftfs mark mount since we always refer back to the lowers mount to get around vfs layering restrictions.

Regression Potential: Limited to shiftfs.

Test Case: Built a kernel with the mentioned fix and ran the reproducer. The issue was not reproducible.

[Christian Brauner (cbrauner)]

See
https://github.com/brauner/ubuntu-unstable/commits/2020-04-10/shiftfs_nesting
for fix.

[Christian Brauner (cbrauner)]

This should preferably be backported to all LTS kernels that support shiftfs.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-eoan' to 'verification-done-eoan'. If the problem still exists, change the tag 'verification-needed-eoan' to 'verification-failed-eoan'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-focal' to 'verification-done-focal'. If the problem still exists, change the tag 'verification-needed-focal' to 'verification-failed-focal'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 5.4.0-31.35

---------------
linux (5.4.0-31.35) focal; urgency=medium

  * focal/linux: 5.4.0-31.35 -proposed tracker (LP: #1877253)

  * Intermittent display blackouts on event (LP: #1875254)
    - drm/i915: Limit audio CDCLK>=2*BCLK constraint back to GLK only

  * Unable to handle kernel pointer dereference in virtual kernel address space
    on Eoan (LP: #1876645)
    - SAUCE: overlayfs: fix shitfs special-casing

linux (5.4.0-30.34) focal; urgency=medium

  * focal/linux: 5.4.0-30.34 -proposed tracker (LP: #1875385)

  * ubuntu/focal64 fails to mount Vagrant shared folders (LP: #1873506)
    - [Packaging] Move virtualbox modules to linux-modules
    - [Packaging] Remove vbox and zfs modules from generic.inclusion-list

  * linux-image-5.0.0-35-generic breaks checkpointing of container
    (LP: #1857257)
    - SAUCE: overlayfs: use shiftfs hacks only with shiftfs as underlay

  * shiftfs: broken shiftfs nesting (LP: #1872094)
    - SAUCE: shiftfs: record correct creator credentials

  * Add debian/rules targets to compile/run kernel selftests (LP: #1874286)
    - [Packaging] add support to compile/run selftests

  * shiftfs: O_TMPFILE reports ESTALE (LP: #1872757)
    - SAUCE: shiftfs: fix dentry revalidation

  * LIO hanging in iscsit_free_session and iscsit_stop_session (LP: #1871688)
    - scsi: target: iscsi: calling iscsit_stop_session() inside
      iscsit_close_session() has no effect

  * [ICL] TC port in legacy/static mode can't be detected due TCCOLD
    (LP: #1868936)
    - SAUCE: drm/i915: Align power domain names with port names
    - SAUCE: drm/i915/display: Move out code to return the digital_port of the aux
      ch
    - SAUCE: drm/i915/display: Add intel_legacy_aux_to_power_domain()
    - SAUCE: drm/i915/display: Split hsw_power_well_enable() into two
    - SAUCE: drm/i915/tc/icl: Implement TC cold sequences
    - SAUCE: drm/i915/tc: Skip ref held check for TC legacy aux power wells
    - SAUCE: drm/i915/tc/tgl: Implement TC cold sequences
    - SAUCE: drm/i915/tc: Catch TC users accessing FIA registers without enable
      aux
    - SAUCE: drm/i915/tc: Do not warn when aux power well of static TC ports
      timeout

  * alsa/sof: external mic can't be deteced on Lenovo and HP laptops
    (LP: #1872569)
    - SAUCE: ASoC: intel/skl/hda - set autosuspend timeout for hda codecs

  * amdgpu kernel errors in Linux 5.4 (LP: #1871248)
    - drm/amd/display: Stop if retimer is not available

  * Focal update: v5.4.34 upstream stable release (LP: #1874111)
    - amd-xgbe: Use __napi_schedule() in BH context
    - hsr: check protocol version in hsr_newlink()
    - l2tp: Allow management of tunnels and session in user namespace
    - net: dsa: mt7530: fix tagged frames pass-through in VLAN-unaware mode
    - net: ipv4: devinet: Fix crash when add/del multicast IP with autojoin
    - net: ipv6: do not consider routes via gateways for anycast address check
    - net: phy: micrel: use genphy_read_status for KSZ9131
    - net: qrtr: send msgs from local of same id as broadcast
    - net: revert default NAPI poll timeout to 2 jiffies
    - net: tun: record RX queue in skb before do_xdp_gener...

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 5.3.0-53.47

---------------
linux (5.3.0-53.47) eoan; urgency=medium

  * eoan/linux: 5.3.0-53.47 -proposed tracker (LP: #1877257)

  * Intermittent display blackouts on event (LP: #1875254)
    - drm/i915: Limit audio CDCLK>=2*BCLK constraint back to GLK only

  * Unable to handle kernel pointer dereference in virtual kernel address space
    on Eoan (LP: #1876645)
    - SAUCE: overlayfs: fix shitfs special-casing

linux (5.3.0-52.46) eoan; urgency=medium

  * eoan/linux: 5.3.0-52.46 -proposed tracker (LP: #1874752)

  * alsa: make the dmic detection align to the mainline kernel-5.6
    (LP: #1871284)
    - ALSA: hda: add Intel DSP configuration / probe code
    - ALSA: hda: fix intel DSP config
    - ALSA: hda: Allow non-Intel device probe gracefully
    - ALSA: hda: More constifications
    - ALSA: hda: Rename back to dmic_detect option
    - [Config] SND_INTEL_DSP_CONFIG=m
    - [packaging] Remove snd-intel-nhlt from modules

  * built-using constraints preventing uploads (LP: #1875601)
    - temporarily drop Built-Using data

  * ubuntu/focal64 fails to mount Vagrant shared folders (LP: #1873506)
    - [Packaging] Move virtualbox modules to linux-modules
    - [Packaging] Remove vbox and zfs modules from generic.inclusion-list

  * linux-image-5.0.0-35-generic breaks checkpointing of container
    (LP: #1857257)
    - SAUCE: overlayfs: use shiftfs hacks only with shiftfs as underlay

  * shiftfs: broken shiftfs nesting (LP: #1872094)
    - SAUCE: shiftfs: record correct creator credentials

  * Add debian/rules targets to compile/run kernel selftests (LP: #1874286)
    - [Packaging] add support to compile/run selftests

  * shiftfs: O_TMPFILE reports ESTALE (LP: #1872757)
    - SAUCE: shiftfs: fix dentry revalidation

  * getitimer returns it_value=0 erroneously (LP: #1349028)
    - [Config] CONTEXT_TRACKING_FORCE policy should be unset

  * 5.3.0-46-generic - i915 - frequent GPU hangs / resets rcs0 (LP: #1872001)
    - drm/i915/execlists: Preempt-to-busy
    - drm/i915/gt: Detect if we miss WaIdleLiteRestore
    - drm/i915/execlists: Always force a context reload when rewinding RING_TAIL

  * alsa/sof: external mic can't be deteced on Lenovo and HP laptops
    (LP: #1872569)
    - SAUCE: ASoC: intel/skl/hda - set autosuspend timeout for hda codecs

  * Eoan update: upstream stable patchset 2020-04-22 (LP: #1874325)
    - ARM: dts: sun8i-a83t-tbs-a711: HM5065 doesn't like such a high voltage
    - bus: sunxi-rsb: Return correct data when mixing 16-bit and 8-bit reads
    - net: vxge: fix wrong __VA_ARGS__ usage
    - hinic: fix a bug of waitting for IO stopped
    - hinic: fix wrong para of wait_for_completion_timeout
    - cxgb4/ptp: pass the sign of offset delta in FW CMD
    - qlcnic: Fix bad kzalloc null test
    - i2c: st: fix missing struct parameter description
    - cpufreq: imx6q: Fixes unwanted cpu overclocking on i.MX6ULL
    - media: venus: hfi_parser: Ignore HEVC encoding for V1
    - firmware: arm_sdei: fix double-lock on hibernate with shared events
    - null_blk: Fix the null_add_dev() error path
    - null_blk: Handle null_add_dev() failures properly
    - null_blk: fix spuri...

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 5.4.0-42.46

---------------
linux (5.4.0-42.46) focal; urgency=medium

  * focal/linux: 5.4.0-42.46 -proposed tracker (LP: #1887069)

  * linux 4.15.0-109-generic network DoS regression vs -108 (LP: #1886668)
    - SAUCE: Revert "netprio_cgroup: Fix unlimited memory leak of v2 cgroups"

linux (5.4.0-41.45) focal; urgency=medium

  * focal/linux: 5.4.0-41.45 -proposed tracker (LP: #1885855)

  * Packaging resync (LP: #1786013)
    - update dkms package versions

  * CVE-2019-19642
    - kernel/relay.c: handle alloc_percpu returning NULL in relay_open

  * CVE-2019-16089
    - SAUCE: nbd_genl_status: null check for nla_nest_start

  * CVE-2020-11935
    - aufs: do not call i_readcount_inc()

  * ip_defrag.sh in net from ubuntu_kernel_selftests failed with 5.0 / 5.3 / 5.4
    kernel (LP: #1826848)
    - selftests: net: ip_defrag: ignore EPERM

  * Update lockdown patches (LP: #1884159)
    - SAUCE: acpi: disallow loading configfs acpi tables when locked down

  * seccomp_bpf fails on powerpc (LP: #1885757)
    - SAUCE: selftests/seccomp: fix ptrace tests on powerpc

  * Introduce the new NVIDIA 418-server and 440-server series, and update the
    current NVIDIA drivers (LP: #1881137)
    - [packaging] add signed modules for the 418-server and the 440-server
      flavours

 -- Khalid Elmously <email address hidden> Thu, 09 Jul 2020 19:50:26 -0400