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 FBIOPUTVSCREENINFO ioctl on /dev/fb*. When doing so, the driver recomputes FIFO arbitration parameters in nv3arb(), using state->mclk_khz (derived from the PRAMDAC MCLK PLL) as a divisor without validating it first.

In a normal setup, state->mclkkhz 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->mclkkhz to become zero. Once nv3getparam() calls nv3arb(), the division by state->mclkkhz 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:nv3arb drivers/video/fbdev/riva/rivahw.c:439 [inline] RIP: 0010:nv3getparam+0x3ab/0x13b0 drivers/video/fbdev/riva/rivahw.c:546 Call Trace: nv3CalcArbitration.constprop.0+0x255/0x460 drivers/video/fbdev/riva/rivahw.c:603 nv3UpdateArbitrationSettings drivers/video/fbdev/riva/rivahw.c:637 [inline] CalcStateExt+0x447/0x1b90 drivers/video/fbdev/riva/rivahw.c:1246 rivaloadvideomode+0x8a9/0xea0 drivers/video/fbdev/riva/fbdev.c:779 rivafbsetpar+0xc0/0x5f0 drivers/video/fbdev/riva/fbdev.c:1196 fbsetvar+0x604/0xeb0 drivers/video/fbdev/core/fbmem.c:1033 dofbioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1109 fbioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1188 __x64sysioctl+0x122/0x190 fs/ioctl.c:856