[Bug 1807077] [NEW] mountall crashes on udev node with missing devname

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Ryan Finnie (fo0bar):

[Impact]

 * udev block nodes without a devname will crash mountall, resulting in
an unbootable system (emergency root shell)

 * While this is not likely to happen in a matched distro/kernel
environment (it was discovered while needing to run a bionic 4.15 kernel
on trusty), it is possible.

 * The code in try_udev_device() assumes a block subsystem will always
have a devname; the SRU patches explicitly check for a devname and
return if null.

[Test Case]

 * HPE DL385 Gen10, Samsung a822 NVMe controller, trusty install

 * Kernels <4.15 (or possibly 4.14) do not expose nvme0c33n1 and do not
trigger the bug.  Tested on 4.13, 4.4 and 3.13.

 * Kernel 4.15 exposes nvme0c33n1 in udev but does not have a devname,
mountall crash ensues.

[Regression Potential]

 * Patch might ignore legitimate block devices on existing
installations.  Unlikely, since the logic path for null devname leads
directly to a program crash.

[Other Info]
 
 * Additional context for Canonical employees: PS4.5 is a trusty backend cloud, but we now have Gen10 hardware incoming (this was discovered while adding new nova-compute hardware).  Older kernels are not usable because Gen10 requires ilorest, which requires a >4.4 kernel (at least artful 4.13 is known good).  So trusty+4.15 is the only viable combination for continued support of the cloud while adding new hardware.  This is done via apt pinning of bionic for the kernel packages, and, mountall notwithstanding, is working fine so far.


Original description:

Running bionic's 4.15 kernel on trusty on an HPE DL385 Gen10 results in
a device node for the NVMe controller,
/devices/pci0000:40/0000:40:03.1/0000:43:00.0/nvme/nvme0/nvme0c33n1
which itself does not have a devname.  When mountall gets to it:

fsck_update: updating check priorities
try_mount: /srv/nova/instances waiting for device
try_udev_device: ignored /dev/loop5 (not yet ready?)
try_udev_device: ignored /dev/loop6 (not yet ready?)
try_udev_device: ignored /dev/loop1 (not yet ready?)
try_udev_device: ignored /dev/loop0 (not yet ready?)
try_udev_device: block (null) (null) (null)

and then crashes, leaving the boot at an emergency root shell.  A
successful scan looks like this for comparison:

try_udev_device: block /dev/sdb (null) (null)
try_udev_device: block /dev/sdb (null) (null)
try_udev_device: block /dev/sda (null) (null)
try_udev_device: block /dev/nvme0n1 ed56e3a9-60f7-4636-85a2-b53137b598e7 (null)
try_udev_device: block /dev/bcache0 756cb2c6-b999-4905-a021-c2e688e81a86 instances

The debdiffs check for a null devname in try_udev_device() and will not
attempt to process it.

** Affects: mountall (Ubuntu)
     Importance: Undecided
         Status: New

-- 
mountall crashes on udev node with missing devname
https://bugs.launchpad.net/bugs/1807077
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