linux-kernel - Regression: firmware/sysfb.c device path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <lLyvPFC_APGHNfyGNHRpQy5izBikkaTPOpHooZIT3fFAoJPquSI31ZMueA99XTdr8ysir3X7O7IMdc6za-0m79vr_claeparHhoRouVgHOI=@proton.me>
Date: Sat, 13 Jul 2024 17:20:17 +0000
From: Tj <tj.iam.tj@...ton.me>
To: Thomas Zimmermann <tzimmermann@...e.de>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "1075713@...s.debian.org" <1075713@...s.debian.org>
Subject: Regression: firmware/sysfb.c device path

The recent commits to add the parent device path broke Debian's kvm based QA workers for testing installer ISOs after a kernel upgrade from v6.8.12 to v6.9.7. For the details:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1075713

It took some time to  track it down since the superficial symptom appeared to involve the QXL driver. It turned out however to be the fbdev driver; specifically the change in the parent device path in sysfs reported between the two kernels:

6.8.12: 

/sys/class/graphics/fb0 -> ../../devices/platform/vesa-framebuffer.0/graphics/fb0

6.9.7:

/sys/class/graphics/fb0 -> ../../devices/pci0000:00/0000:00:01.0/vesa-framebuffer.0/graphics/fb0

This breaks xserver-xorg-core's libfbdevhw.so because it differentiates code-paths based on whether "devices/pci" is matched in the symlink.

See hw/xfree86/fbdevhw/fbdevhw.c::fbdev_open()

https://gitlab.freedesktop.org/xorg/xserver/-/blob/master/hw/xfree86/fbdevhw/fbdevhw.c?ref_type=heads#L381