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 Code: c1 e8 03 42 0f b6 14 38 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 b7 0e 00 00 41 8b 46 18 01 d8 69 c0 40 42 0f 00 99 <41> f7 fc 48 63 c8 4c 89 e8 48 c1 e8 03 42 0f b6 14 38 4c 89 e8 83 RSP: 0018:ffff888013b2f318 EFLAGS: 00010206 RAX: 0000000001d905c0 RBX: 0000000000000016 RCX: 0000000000040000 RDX: 0000000000000000 RSI: 0000000000000080 RDI: ffff888013b2f6f0 RBP: 0000000000000002 R08: ffffffff82226288 R09: 0000000000000001 R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000 R13: ffff888013b2f4d8 R14: ffff888013b2f6d8 R15: dffffc0000000000 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

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Guangshuo Li lgs201920130244@gmail.com --- drivers/video/fbdev/riva/riva_hw.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/drivers/video/fbdev/riva/riva_hw.c b/drivers/video/fbdev/riva/riva_hw.c index 8b829b720064..d70c6c4d28e8 100644 --- a/drivers/video/fbdev/riva/riva_hw.c +++ b/drivers/video/fbdev/riva/riva_hw.c @@ -436,6 +436,9 @@ static char nv3_arb(nv3_fifo_info * res_info, nv3_sim_state * state, nv3_arb_in vmisses = 2; eburst_size = state->memory_width * 1; mburst_size = 32; + if (!state->mclk_khz) + return (0); + gns = 1000000 * (gmisses*state->mem_page_miss + state->mem_latency)/state->mclk_khz; ainfo->by_gfacc = gns*ainfo->gdrain_rate/1000000; ainfo->wcmocc = 0;