Bug 2093668

Summary: lightdm: xauthority corruption
Product: [Fedora] Fedora EPEL Reporter: k_sinoha
Component: lightdmAssignee: Alternative GTK desktop environments <alt-gtk-de-sig>
Status: CLOSED ERRATA QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: high Docs Contact:
Priority: unspecified    
Version: epel8CC: alt-gtk-de-sig, christoph.wickert, fedora, gp, k_sinoha, leigh123linux, rdieter, tdawson
Target Milestone: ---   
Target Release: ---   
Hardware: All   
OS: All   
Whiteboard:
Fixed In Version: lightdm-1.32.0-1.fc37 Doc Type: ---
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2022-07-18 10:43:09 UTC Type: Bug
Regression: --- Mount Type: ---
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Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Description k_sinoha 2022-06-05 05:52:40 UTC 
Description of problem:
No O_TRUNC causes the xauthority file corruption.
In case the address of XDMCP DISPLAY length differs.
1st access came from "192.168.1.1:1".
2nd access came from "hostname.com:2".
And close 1st access.
The result of # xauth -f /var/run/lightdm/lightdm/xauthority list is as follows.
hostname/unix0 MIT-MAGIC-COOKIE-1 xxxxxxxx.
hostname.com:2 MIT-MAGIC-COOKIE-1 yyyyyyyy.

And next access from "192.168.1.2:2"
hostname/unix0 MIT-MAGIC-COOKIE-1 xxxxxxx...x.
hostname.com:2 MIT-MAGIC-COOKIE-1 yyyyy...yyy.
192.168.1.2:2 MIT-MAGIC-COOKIE-1 zzzzzzz...zz.

And close the session from "hostname.com:2" will cause the corruption.
hostname/unix0 MIT-MAGIC-COOKIE-1 xxxxxxx...x.
192.168.1.2:2 MIT-MAGIC-COOKIE-1 zzzzzzz...zz.
#$weq321% 3 44ddaawe3we12312421412z.

This is because, without O_TRUNC will open original file itself, REMOVE will delete the entry of hostname.com:2 , but the length is too big to 192.168.1.2:2.

Version-Release number of selected component (if applicable):


How reproducible:
No O_TRUNC causes the xauthority file corruption.
In case the address of XDMCP DISPLAY length differs.

Steps to Reproduce:
1.Access from IPv4 address.
2.Access from FQDN resolvable hostname.
3.Then xauthority will corruopt.

How to fix this problem:
  src/xauthority.c
 now:
    int output_fd = g_open (filename, O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
 FIXED:
    int output_fd = g_open (filename, O_WRONLY | O_CREAT | O_TRUNC , S_IRUSR | S_IWUSR);
--
This pull request has already merged cannonical/lightdm.
https://github.com/canonical/lightdm/pull/202
Comment 1 Fedora Update System 2022-07-18 10:39:58 UTC 
FEDORA-2022-088850eb6f has been submitted as an update to Fedora 37. https://bodhi.fedoraproject.org/updates/FEDORA-2022-088850eb6f
Comment 2 Fedora Update System 2022-07-18 10:43:09 UTC 
FEDORA-2022-088850eb6f has been pushed to the Fedora 37 stable repository.
If problem still persists, please make note of it in this bug report.