CVE-2025-38198 — fbcon: Make sure modelist not set on unregistered console

Affected: Linux, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP, Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

In the Linux kernel, the following vulnerability has been resolved:

fbcon: Make sure modelist not set on unregistered console

It looks like attempting to write to the "store_modes" sysfs node will run afoul of unregistered consoles:

UBSAN: array-index-out-of-bounds in drivers/video/fbdev/core/fbcon.c:122:28 index -1 is out of range for type 'fb_info *[32]' ... fbcon_info_from_console+0x192/0x1a0 drivers/video/fbdev/core/fbcon.c:122 fbcon_new_modelist+0xbf/0x2d0 drivers/video/fbdev/core/fbcon.c:3048 fb_new_modelist+0x328/0x440 drivers/video/fbdev/core/fbmem.c:673 store_modes+0x1c9/0x3e0 drivers/video/fbdev/core/fbsysfs.c:113 dev_attr_store+0x55/0x80 drivers/base/core.c:2439

static struct fb_info *fbcon_registered_fb[FB_MAX]; ... static signed char con2fb_map[MAX_NR_CONSOLES]; ... static struct fb_info *fbcon_info_from_console(int console) ... return fbcon_registered_fb[con2fb_map[console]];

If con2fb_map contains a -1 things go wrong here. Instead, return NULL, as callers of fbcon_info_from_console() are trying to compare against existing "info" pointers, so error handling should kick in correctly.

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CVE-2025-38198 — fbcon: Make sure modelist not set on unregistered console