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Bug 1798702

Summary: shm busted in mesa again
Product: Red Hat Enterprise Linux 8 Reporter: Ray Strode [halfline] <rstrode>
Component: mesaAssignee: Dave Airlie <airlied>
Status: CLOSED ERRATA QA Contact: Desktop QE <desktop-qa-list>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 8.2CC: airlied, jkoten, modehnal, tpelka
Target Milestone: rcKeywords: Regression
Target Release: 8.0Flags: pm-rhel: mirror+
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: mesa-19.3.4-2.el8 Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2020-04-28 15:41:41 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1739559    

Description Ray Strode [halfline] 2020-02-05 19:58:45 UTC
If I do something like

Xephyr -query localhost :123

when XDMCP is enabled, all windows show up black with clear titlebars.

This is the same symptom we've had in the past when the SHM detection in mesa was broken iirc.

Indeed,

Xephyr -extension mit-shm -query localhost :123

works around the problem.

Maybe dropped patch in a rebase?

Comment 1 Michal Odehnal 2020-02-07 09:47:28 UTC
*** Bug 1800486 has been marked as a duplicate of this bug. ***

Comment 2 Dave Airlie 2020-02-13 05:09:02 UTC
reproduced this locally.

Comment 3 Dave Airlie 2020-02-13 05:28:05 UTC
small analysis

upstream did a CVE fix to make shm segment permissions 600 instead of 777 to stop random users accessing them

running Xephyr as user 1000, but then having a user session inside it running as user 1001 stops the shm from being accessed.

commit addf63dbd796fc08e06ac1323071a8f8f48ac7b9
Author: Brian Paul <brianp>
Date:   Wed Oct 9 12:05:16 2019 -0600

    Call shmget() with permission 0600 instead of 0777
    
    A security advisory (TALOS-2019-0857/CVE-2019-5068) found that
    creating shared memory regions with permission mode 0777 could allow
    any user to access that memory.  Several Mesa drivers use shared-
    memory XImages to implement back buffers for improved performance.
    
    This path changes the shmget() calls to use 0600 (user r/w).
    
    Tested with legacy Xlib driver and llvmpipe.
    
    Cc: mesa-stable.org
    Reviewed-by: Kristian H. Kristensen <hoegsberg>
    (cherry picked from commit 02c3dad0f3b4d26e0faa5cc51d06bc50d693dcdc)

Comment 4 Dave Airlie 2020-02-14 05:15:47 UTC
https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3823

Upstream proposed fixes.

Comment 5 Dave Airlie 2020-02-14 21:30:13 UTC
mesa-19.3.4-1.el8 built in brew

Comment 8 Ray Strode [halfline] 2020-02-17 16:03:43 UTC
*** Bug 1779994 has been marked as a duplicate of this bug. ***

Comment 9 Michal Odehnal 2020-02-18 08:21:05 UTC
I can still reproduce to some extent. Windows are no longer black, but gnome-shell panels are still broken.

Comment 10 Dave Airlie 2020-02-18 23:35:29 UTC
Hey Michal,

I'm not reproducing that at all here in a VM with qxl, can you drop drop a screenshot here or what panels are broken?

or maybe just test RHEL 8.1 baseline with just the mesa package updated (if you are not), as I'm seeing not great stability with RHEL8.2 nightly.

Comment 11 Michal Odehnal 2020-02-19 09:41:23 UTC
Hi, I am seeing exact issues with panels that shows in video attachment in duplicate bug here https://bugzilla.redhat.com/show_bug.cgi?id=1800486. I used the Rey's reproducer here, using Xephyr, logging in and playing with panels. I also tried with base RHEL8.1 with updated only mesa, same issue.

Comment 12 Michal Odehnal 2020-02-19 09:46:43 UTC
Now I noticed I had vga model set, switched to qxl but the issue still remains.

Comment 13 Dave Airlie 2020-02-19 19:46:24 UTC
okay thanks for that, I was missing what you are seeing, looks like another bug in the fallback paths, will dig a bit more today.

Comment 14 Tomas Pelka 2020-02-20 07:23:55 UTC
Michale please check the new build in brew.

Comment 15 Michal Odehnal 2020-02-20 07:46:52 UTC
All works as expected now.

Comment 17 errata-xmlrpc 2020-04-28 15:41:41 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:1633