CVE-2026-23266

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

fbdev: rivafb: fix divide error in nv3_arb()

A userspace program can trigger the RIVA NV3 arbitration code by calling

the FBIOPUT_VSCREENINFO ioctl on /dev/fb*. When doing so, the driver

recomputes FIFO arbitration parameters in nv3_arb(), using state->mclk_khz

(derived from the PRAMDAC MCLK PLL) as a divisor without validating it

first.

In a normal setup, state->mclk_khz is provided by the real hardware and is

non-zero. However, an attacker can construct a malicious or misconfigured

device (e.g. a crafted/emulated PCI device) that exposes a bogus PLL

configuration, causing state->mclk_khz to become zero. Once

nv3_get_param() calls nv3_arb(), the division by state->mclk_khz in the gns

calculation causes a divide error and crashes the kernel.

Fix this by checking whether state->mclk_khz is zero and bailing out before

doing the division.

The following log reveals it:

rivafb: setting virtual Y resolution to 2184

divide error: 0000 [#1] PREEMPT SMP KASAN PTI

CPU: 0 PID: 2187 Comm: syz-executor.0 Not tainted 5.18.0-rc1+ #1

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014

RIP: 0010:nv3_arb drivers/video/fbdev/riva/riva_hw.c:439 [inline]

RIP: 0010:nv3_get_param+0x3ab/0x13b0 drivers/video/fbdev/riva/riva_hw.c:546

Call Trace:

nv3CalcArbitration.constprop.0+0x255/0x460 drivers/video/fbdev/riva/riva_hw.c:603

nv3UpdateArbitrationSettings drivers/video/fbdev/riva/riva_hw.c:637 [inline]

CalcStateExt+0x447/0x1b90 drivers/video/fbdev/riva/riva_hw.c:1246

riva_load_video_mode+0x8a9/0xea0 drivers/video/fbdev/riva/fbdev.c:779

rivafb_set_par+0xc0/0x5f0 drivers/video/fbdev/riva/fbdev.c:1196

fb_set_var+0x604/0xeb0 drivers/video/fbdev/core/fbmem.c:1033

do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1109

fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1188

__x64_sys_ioctl+0x122/0x190 fs/ioctl.c:856