Bug#927395: Do not touch(1) update-exim4.conf.conf for no good reason

[Marc Haber]

severity #927395 wishlist
thanks

On Thu, Apr 18, 2019 at 09:44:05PM +0800, 積丹尼 Dan Jacobson wrote:
> $ cat /var/log/apt/history.log
> Start-Date: 2019-04-18  01:32:49
> Upgrade: exim4-base:amd64 (4.92-5, 4.92-6), openssl:amd64 (1.1.1b-1, 1.1.1b-2), unicode-data:amd64 (12.0.0-1, 12.1.0~pre1-1), exim4-daemon-light:amd64 (4.92-5, 4.92-6), rsyslog:amd64 (8.1903.0-4, 8.1904.0-1), exim4-config:amd64 (4.92-5, 4.92-6), exim4:amd64 (4.92-5, 4.92-6), libssl1.1:amd64 (1.1.1b-1, 1.1.1b-2), libfaad2:amd64 (2.8.8-1, 2.8.8-2)
> End-Date: 2019-04-18  01:32:56
> 
> some process did a touch(1) or otherwise changing
> $ stat /etc/exim4/update-exim4.conf.conf
>   File: /etc/exim4/update-exim4.conf.conf
>   Size: 1154            Blocks: 8          IO Block: 4096   regular file
> Device: 803h/2051d      Inode: 524387      Links: 1
> Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
> Modify: 2019-04-18 01:32:53.473019451 +0800 <------------THIS
> Change: 2019-04-18 01:32:53.477019558 +0800

Tihs is probably the debconf-driven generation of ue4cc that happens
during package upgrades. Things have always been that way, and I bet
that a hundred other packages do the same thing. The file belongs to the
package and IMO it is ok to expect that a file that belongs to a
package changes during an update.

To avoid this, one would need to write the output to
update.exim4.conf.conf.temp, compare checksums and only move the temp
file to the real file if they are different. This probably opens the
possibility of five insecure temp file name, cruft left around bugs and
in addition a bunch of nice race conditions. I am unsure whether this is
really worth the trouble.

> causing alarm bells to ring on my homebrew security system.

Local problem ;-)  lowering severity.

> (Plus I bet it is a policy violation.)

citation needed

Greetings
Marc

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