Bug#1082905: exim4-daemon-light: crash at dkim.c:745 when dkim_private_key is not readable by exim4 process

[Andreas Metzler]

On 2024-09-28 Germano Leichsenring <germano.leichsenring at gmail.com> wrote:
[...]
> I've followed upstream instructions to setup DKIM.
> https://exim.org/exim-html-4.93/doc/html/spec_html/ch-dkim_spf_and_dmarc.html
>  Note, the command below creates the private key file with permissions 600.
> $ openssl genpkey -algorithm ed25519 -out dkim_ed25519.private

>    * What was the outcome of this action?
>  Accordingly, exim4 process crashed and left a stacktrace in the paniclog.
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S SIGSEGV (fault address: 0x55fac168b1d0)
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S SEGV_ACCERR
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S SIGSEGV (maybe attempt to write to immutable memory)
> )
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S backtrace
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S ---
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S 	/usr/sbin/exim4(+0x5b1cd) [0x55faaf6381cd]
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S 	/usr/sbin/exim4(+0x5b394) [0x55faaf638394]
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S 	/lib/x86_64-linux-gnu/libc.so.6(+0x3f5d0) [0x7f34f66545d0]
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S 	/usr/sbin/exim4(+0x72f6a) [0x55faaf64ff6a]
> 2024-09-28 10:33:46 1suML0-00000001hFO-444S 	/usr/sbin/exim4(+0x739e4) [0x55faaf6509e4]

>  After looking at the faulty line (dkim.c:745) I've realized that the file was not readable.
[...]

Hello Germano,

I could not reproduce this. I set up dkim signing, verified that it
worked by sending a test message and ran chmod 0000 on the key files.
All I got was an error message in mainlog and panic log (unable to open
file for reading) but no crash.

How did you come up with the diagnosis that dkim.c:745 was the faulty
line? (Please feel free to directly respond on
https://bugs.exim.org/show_bug.cgi?id=3116 )

cu Andreas
-- 
`What a good friend you are to him, Dr. Maturin. His other friends are
so grateful to you.'
`I sew his ears on from time to time, sure'