Bug#891936: [Pkg-zfsonlinux-devel] Bug#891936: zfs-dkms: 32/64-bit detection via /proc/kallsyms is a bad idea

[Aron Xu]

Hi,

On Sat, Mar 3, 2018 at 2:52 AM, Fabian Grünbichler
 wrote:
> Package: zfs-dkms
> Version: 0.7.6-1
> Severity: normal
>
> the zfs-dkms package tries to detect whether the (running) kernel is a
> 32-bit or 64-bit one with the following stanza (in zfs-dkms.config /
> zfs-dkms.postinst):
>
> $ head -1 /proc/kallsyms|awk '{print $1}'|wc -c
>
> and checking the length of the resulting string.
>
> if the check fails or reports a 32-bit kernel, the user is prompted via
> debconf whether the build should be aborted.
>
> both the check and the resulting actions is wrong and should likely be
> dropped altogether:
> - kallsyms recently got more restrictive and does not print address for
>   all entries. the recent 4.15 kernel uploaded to sid has two lines
>   starting with "  (null)" at the top, which breaks the check
> - kallsyms might be disabled (in a custom kernel build)
> - the running kernel is not necessarily the (only) one that dkms builds for
> - ZFS supports 32-bit (although with a footnote about potential
>   address space related stability problems)
>
> if this check is still desired, it should probably be fixed and made
> more smart and check the actual kernel sources that dkms will build
> with.
>

I prefer to keep the check because 32-bit kernels are never
first-class citizens in the world of ZFS, even if it builds and works
at most cases.

On conventional hardware (say, x86 workstations and servers),
deliberately using a 32-bit kernel is rare; for other purposes user
should evaluate the risks themselves before deciding on storage
choice.

Regards,
Aron

Bug#891936: [zfs-dkms]

[Antonio Russo]

Control: tag -1 patch

The most widespread symptom can be fixed with a little bit of
grep hackery (patch attached). This fixes the "some/all lines
starting with ' *(null)'" case, though I haven't tested this
on any 32-bit machines (I don't have any).
commit e56332bf68aa71e22e13f7294f7587a202c7b68a
Author: Antonio Russo 
Date:   Fri Mar 2 17:05:22 2018 -0500

Handle /proc/kallsym obfuscation

diff --git a/debian/zfs-dkms.postinst b/debian/zfs-dkms.postinst
index cb87e1ce..0ecb9674 100644
--- a/debian/zfs-dkms.postinst
+++ b/debian/zfs-dkms.postinst
@@ -6,7 +6,7 @@ set -e
 
 kernelbits=unknown
 if [ -r /proc/kallsyms ]; then
-	addrlen=$(head -1 /proc/kallsyms|awk '{print $1}'|wc -c)
+	addrlen=$(head -1 /proc/kallsyms| grep -o '^ *[^ ]*' |wc -c)
 	if [ $addrlen = 17 ]; then
 		kernelbits=64
 	elif [ $addrlen = 9 ]; then

Bug#891936: zfs-dkms: 32/64-bit detection via /proc/kallsyms is a bad idea

[Fabian Grünbichler]

Package: zfs-dkms
Version: 0.7.6-1
Severity: normal

the zfs-dkms package tries to detect whether the (running) kernel is a
32-bit or 64-bit one with the following stanza (in zfs-dkms.config /
zfs-dkms.postinst):

$ head -1 /proc/kallsyms|awk '{print $1}'|wc -c

and checking the length of the resulting string.

if the check fails or reports a 32-bit kernel, the user is prompted via
debconf whether the build should be aborted.

both the check and the resulting actions is wrong and should likely be
dropped altogether:
- kallsyms recently got more restrictive and does not print address for
  all entries. the recent 4.15 kernel uploaded to sid has two lines
  starting with "  (null)" at the top, which breaks the check
- kallsyms might be disabled (in a custom kernel build)
- the running kernel is not necessarily the (only) one that dkms builds for
- ZFS supports 32-bit (although with a footnote about potential
  address space related stability problems)

if this check is still desired, it should probably be fixed and made
more smart and check the actual kernel sources that dkms will build
with.

-- System Information:
Debian Release: buster/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'unstable'), (500, 'testing'), 
(500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.15.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), 
LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages zfs-dkms depends on:
ii  debconf [debconf-2.0]  1.5.66
ii  dkms   2.3-3
ii  lsb-release9.20170808
ii  spl-dkms   0.7.6-1

Versions of packages zfs-dkms recommends:
ii  linux-libc-dev  4.15.4-1
ii  zfs-zed 0.7.6-1
ii  zfsutils-linux  0.7.6-1

zfs-dkms suggests no packages.

-- debconf information excluded
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