implement errno action logging in seccomp for strict mode with snaps

Bug #1721676 reported by Tyler Hicks on 2017-10-06
14
This bug affects 2 people
Affects Status Importance Assigned to Milestone
Snappy
Medium
Tyler Hicks
linux (Ubuntu)
Undecided
Tyler Hicks
Xenial
Undecided
Tyler Hicks
Zesty
Undecided
Tyler Hicks
Artful
Undecided
Tyler Hicks

Bug Description

A requirement for snappy is that security sandbox violations against policy are logged. In this manner learning tools can be written to parse the logs, etc and make developing on snappy easier.

The current default seccomp action, in strict mode. is to kill the snap's thread that violated the policy but this is unfriendly to the developer and to the user. The desired action is to block the illegal system call and return an error with errno set to EPERM. However, seccomp does not emit log events when it takes that action. Seccomp should be updated to emit log events when taking the SECCOMP_RET_ERRNO action and then snappy can switch to the using that action when blocking illegal system calls.

[Impact]

Snapd needs a way to log SECCOMP_RET_ERRNO seccomp actions in order to have a more friendly strict mode. Such functionality has been merged upstream into 4.14-rc2.

No libseccomp changes are needed at this time since snap-confine loads the BPF filter directly into the kernel without using libseccomp.

[Test Case]

Running the libseccomp "live" tests will exercise the kernel's seccomp enforcement and help to help catch any regressions. Note that on Artful, there's an existing test failure (20-live-basic_die%%002-00001):

$ sudo apt build-dep -y libseccomp
$ sudo apt install -y cython
$ apt source libseccomp
$ cd libseccomp-*
$ autoreconf -ivf && ./configure --enable-python && make check-build
$ (cd tests && ./regression -T live)

All tests should pass on zesty (12 tests) and xenial (10 tests). On artful, you'll see one pre-existing failure:
...
Test 20-live-basic_die%%002-00001 result: FAILURE 20-live-basic_die TRAP rc=159
...
Regression Test Summary
 tests run: 12
 tests skipped: 0
 tests passed: 11
 tests failed: 1
 tests errored: 0
============================================================

----------------------------

Running the seccomp kernel selftests is also a great to exercise seccomp and the kernel patch set proposed for the SRU includes additional seccomp selftests. To build, enter into the root of the kernel source tree and build the seccomp test binary:

$ make -C tools/testing/selftests TARGETS=seccomp

Now you can execute tools/testing/selftests/seccomp/seccomp_bpf or even copy it to a test machine and run it there. On Xenial, 54/54 tests should pass and 58/58 should pass on Zesty.

----------------------------

Now we can run a single test to verify that SECCOMP_RET_ERRNO is logged when the application opts into it. First, verify that "errno" is listed in the actions_logged sysctl:

$ cat /proc/sys/kernel/seccomp/actions_logged
kill trap errno trace log

Now, build and run the test program:

$ gcc -o lp1721676-kernel-test lp1721676-kernel-test.c
$ ./lp1721676-kernel-test
SUCCESS: getpid() failed as expected: Operation not permitted

It should have generated a message like this in /var/log/syslog:

kernel: [79338.804966] audit: type=1326 audit(1507259221.875:27): auid=1000 uid=1000 gid=1000 ses=5 pid=3091 comm="lp1721676-kerne" exe="/home/tyhicks/lp1721676-kernel-test" sig=0 arch=c000003e syscall=39 compat=0 ip=0x7fb91829c499 code=0x50000

Disable errno logging in the sysctl:

$ echo kill trap trace log | sudo tee /proc/sys/kernel/seccomp/actions_logged
kill trap trace log

Rerun the test program and ensure that nothing was logged this time.

[Regression Potential]

The kernel patches received a lot of review between Kees and some others interested in improved seccomp logging. I authored the patches and feel comfortable/confident with my backported versions. They do not change the behavior of seccomp logging by default but offer ways applications to opt into more logging and, on the flipside, ways for the administrator to quite any additional logging.

Tyler Hicks (tyhicks) on 2017-10-06
Changed in linux (Ubuntu Xenial):
status: New → In Progress
assignee: nobody → Tyler Hicks (tyhicks)
Changed in linux (Ubuntu Zesty):
status: New → In Progress
assignee: nobody → Tyler Hicks (tyhicks)
Changed in linux (Ubuntu Artful):
status: New → Fix Released
assignee: nobody → Tyler Hicks (tyhicks)
Tyler Hicks (tyhicks) wrote :

The kernel patches for this feature have already been released in an Artful kernel (4.12.0-13.14).

description: updated
Tyler Hicks (tyhicks) on 2017-10-06
description: updated
Tyler Hicks (tyhicks) on 2017-10-06
description: updated
Changed in linux (Ubuntu Xenial):
status: In Progress → Fix Committed
Changed in linux (Ubuntu Zesty):
status: In Progress → Fix Committed
Tyler Hicks (tyhicks) wrote :

Here's the kernel test case that I mentioned in the bug description.

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-xenial' to 'verification-done-xenial'. If the problem still exists, change the tag 'verification-needed-xenial' to 'verification-failed-xenial'.

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!

tags: added: verification-needed-xenial
tags: added: verification-needed-zesty

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-zesty' to 'verification-done-zesty'. If the problem still exists, change the tag 'verification-needed-zesty' to 'verification-failed-zesty'.

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!

Tyler Hicks (tyhicks) wrote :

I tested the linux kernel SRU in Xenial and Zesty using the following linux package versions:

 - xenial: linux-image-4.4.0-98-generic 4.4.0-98.121
 - zesty: linux-image-4.10.0-38-generic 4.10.0-38.42

The linux kernel SRU testing was successful and followed what's documented in the [Test Case] section of this bug description.

tags: added: verification-done-xenial verification-done-zesty
removed: verification-needed-xenial verification-needed-zesty
Launchpad Janitor (janitor) wrote :
Download full text (4.4 KiB)

This bug was fixed in the package linux - 4.10.0-38.42

---------------
linux (4.10.0-38.42) zesty; urgency=low

  * linux: 4.10.0-38.42 -proposed tracker (LP: #1722330)

  * Controller lockup detected on ProLiant DL380 Gen9 with P440 Controller
    (LP: #1720359)
    - scsi: hpsa: limit transfer length to 1MB

  * [Dell Docking IE][0bda:8153] Realtek USB Ethernet leads to system hang
    (LP: #1720977)
    - r8152: fix the list rx_done may be used without initialization

  * Touchpad not detected in Lenovo X1 Yoga / Yoga 720-15IKB (LP: #1700657)
    - mfd: intel-lpss: Add missing PCI ID for Intel Sunrise Point LPSS devices

  * Add installer support for Broadcom BCM573xx network drivers. (LP: #1720466)
    - d-i: Add bnxt_en to nic-modules.

  * CVE-2017-1000252
    - KVM: VMX: Do not BUG() on out-of-bounds guest IRQ

  * CVE-2017-10663
    - f2fs: sanity check checkpoint segno and blkoff

  * xfstest sanity checks on seek operations fails (LP: #1696049)
    - xfs: fix off-by-one on max nr_pages in xfs_find_get_desired_pgoff()

  * [P9, Power NV][ WSP][Ubuntu 16.04.03] : perf hw breakpoint command results
    in call traces and system goes for reboot. (LP: #1706033)
    - powerpc/64s: Handle data breakpoints in Radix mode

  * 5U84 - ses driver isn't binding right - cannot blink lights on 1 of the 2
    5u84 (LP: #1693369)
    - scsi: ses: do not add a device to an enclosure if enclosure_add_links()
      fails.

  * Vlun resize request could fail with cxlflash driver (LP: #1713575)
    - scsi: cxlflash: Fix vlun resize failure in the shrink path

  * More migrations with constant load (LP: #1713576)
    - sched/fair: Prefer sibiling only if local group is under-utilized

  * New PMU fixes for marked events. (LP: #1716491)
    - powerpc/perf: POWER9 PMU stops after idle workaround

  * CVE-2017-14340
    - xfs: XFS_IS_REALTIME_INODE() should be false if no rt device present

  * [Zesty][Yakkety] rtl8192e bug fixes (LP: #1698470)
    - staging: rtl8192e: rtl92e_fill_tx_desc fix write to mapped out memory.
    - staging: rtl8192e: fix 2 byte alignment of register BSSIDR.
    - staging: rtl8192e: rtl92e_get_eeprom_size Fix read size of EPROM_CMD.
    - staging: rtl8192e: GetTs Fix invalid TID 7 warning.

  * Stranded with ENODEV after mdadm --readonly (LP: #1706243)
    - md: MD_CLOSING needs to be cleared after called md_set_readonly or
      do_md_stop

  * multipath -ll is not showing the disks which are actually multipath
    (LP: #1718397)
    - fs: aio: fix the increment of aio-nr and counting against aio-max-nr

  * ETPS/2 Elantech Touchpad inconsistently detected (Gigabyte P57W laptop)
    (LP: #1594214)
    - Input: i8042 - add Gigabyte P57 to the keyboard reset table

  * CVE-2017-10911
    - xen-blkback: don't leak stack data via response ring

  * CVE-2017-11176
    - mqueue: fix a use-after-free in sys_mq_notify()

  * implement 'complain mode' in seccomp for developer mode with snaps
    (LP: #1567597)
    - Revert "UBUNTU: SAUCE: seccomp: log actions even when audit is disabled"
    - seccomp: Provide matching filter for introspection
    - seccomp: Sysctl to display available actions
    - seccomp: Operation for checking if an a...

Read more...

Changed in linux (Ubuntu Zesty):
status: Fix Committed → Fix Released
Launchpad Janitor (janitor) wrote :
Download full text (11.5 KiB)

This bug was fixed in the package linux - 4.4.0-98.121

---------------
linux (4.4.0-98.121) xenial; urgency=low

  * linux: 4.4.0-98.121 -proposed tracker (LP: #1722299)

  * Controller lockup detected on ProLiant DL380 Gen9 with P440 Controller
    (LP: #1720359)
    - scsi: hpsa: limit transfer length to 1MB

  * [Dell Docking IE][0bda:8153] Realtek USB Ethernet leads to system hang
    (LP: #1720977)
    - r8152: fix the list rx_done may be used without initialization

  * Add installer support for Broadcom BCM573xx network drivers. (LP: #1720466)
    - d-i: Add bnxt_en to nic-modules.

  * snapcraft.yaml: add dpkg-dev to the build deps (LP: #1718886)
    - snapcraft.yaml: add dpkg-dev to the build deps

  * Support setting I2C_TIMEOUT via ioctl for i2c-designware (LP: #1718578)
    - i2c: designware: Use transfer timeout from ioctl I2C_TIMEOUT

  * 5U84 - ses driver isn't binding right - cannot blink lights on 1 of the 2
    5u84 (LP: #1693369)
    - scsi_transport_sas: add function to get SAS endpoint address
    - ses: fix discovery of SATA devices in SAS enclosures
    - scsi: sas: provide stub implementation for scsi_is_sas_rphy
    - scsi: ses: Fix SAS device detection in enclosure

  * multipath -ll is not showing the disks which are actually multipath
    (LP: #1718397)
    - fs: aio: fix the increment of aio-nr and counting against aio-max-nr

  * Support Dell Wireless DW5819/5818 WWAN devices (LP: #1721455)
    - SAUCE: USB: serial: qcserial: add Dell DW5818, DW5819

  * CVE-2017-10911
    - xen-blkback: don't leak stack data via response ring

  * implement 'complain mode' in seccomp for developer mode with snaps
    (LP: #1567597)
    - seccomp: Provide matching filter for introspection
    - seccomp: Sysctl to display available actions
    - seccomp: Operation for checking if an action is available
    - seccomp: Sysctl to configure actions that are allowed to be logged
    - seccomp: Selftest for detection of filter flag support
    - seccomp: Action to log before allowing

  * implement errno action logging in seccomp for strict mode with snaps
    (LP: #1721676)
    - seccomp: Provide matching filter for introspection
    - seccomp: Sysctl to display available actions
    - seccomp: Operation for checking if an action is available
    - seccomp: Sysctl to configure actions that are allowed to be logged
    - seccomp: Selftest for detection of filter flag support
    - seccomp: Filter flag to log all actions except SECCOMP_RET_ALLOW

  * [Xenial] update OpenNSL kernel modules to 6.5.10 (LP: #1721511)
    - SAUCE: update OpenNSL kernel modules to 6.5.10

  * Xenial update to 4.4.90 stable release (LP: #1721550)
    - cifs: release auth_key.response for reconnect.
    - mac80211: flush hw_roc_start work before cancelling the ROC
    - KVM: PPC: Book3S: Fix race and leak in kvm_vm_ioctl_create_spapr_tce()
    - tracing: Fix trace_pipe behavior for instance traces
    - tracing: Erase irqsoff trace with empty write
    - md/raid5: fix a race condition in stripe batch
    - md/raid5: preserve STRIPE_ON_UNPLUG_LIST in break_stripe_batch_list
    - scsi: scsi_transport_iscsi: fix the issue that iscsi_if_rx doesn't parse
      nlms...

Changed in linux (Ubuntu Xenial):
status: Fix Committed → Fix Released
Tyler Hicks (tyhicks) wrote :

The snapd pull request is located here: https://github.com/snapcore/snapd/pull/3998/

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