diff options
| author | Guangshuo Li <lgs201920130244@gmail.com> | 2025-12-07 15:25:32 +0800 |
|---|---|---|
| committer | Helge Deller <deller@gmx.de> | 2026-02-14 11:07:12 +0100 |
| commit | 0209e21e3c372fa2da04c39214bec0b64e4eb5f4 (patch) | |
| tree | 9522b1f7cc90cb78c3bb93e3e2b414da98f9ce39 | |
| parent | 770aaedb461a055f79b971d538678942b6607894 (diff) | |
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
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
| -rw-r--r-- | drivers/video/fbdev/riva/riva_hw.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/drivers/video/fbdev/riva/riva_hw.c b/drivers/video/fbdev/riva/riva_hw.c index 8b829b720064..f292079566cf 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; |