Is Samba AIO affected by recent Linux data corruption bug?

[Bram Matthys]

Hi everyone,

In relation to the recent Linux filesystem corruption bug with O_DIRECT 
[1]. I read that to trigger this, an application needs to use O_DIRECT 
and that the bug is that the file position is not updated properly. So 
the bug does not happen with pwrite(), or if lseek() is always called prior.

My questin: would this bug be triggered by Samba? I know Samba does AIO 
and that it is enabled by default (i have it on too). But I see heavy 
use of pwrite(). Does that mean things are safe? Or does it also use 
O_DIRECT without pwrite/lseek as well.

Would love to hear from a samba dev or someone who otherwise is familiar 
with this part of the code, to be sure. It is hard for me as an outsider 
to judge/audit the code in such a short timeframe and so easy to miss 
something.

The reason is, I missed the word on this filesystem corruption issue and 
due to an unfortunate timing (system maintenance with a reboot to the 
affected kernel last weekend) we had a production machine running 3 days 
with the affected kernel. As for Samba, we are on 4.18.8.

Of course I have been doing a quick compare with last safe backup but 
sadly that is of limited use. It only shows what files have changed but 
not if the change is among one of the many legit changes or a case of 
file corruption. So far I have zero indications of corruption but it 
would be so much better to know if Samba would trigger this bug or not. 
I can imagine the Samba team would have had similar questions, if not on 
list then from customers directly, in the past week or so.

Thanks in advance,

Bram Matthys

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1057843 and 
https://lore.kernel.org/stable/20231205122122.dfhhoaswsfscuhc3@quack3/ etc.