From 13ef2706360385794db28119420ed67d0a88e00f Mon Sep 17 00:00:00 2001 From: Zheyu Ma Date: Wed, 3 Aug 2022 17:23:12 +0800 Subject: [PATCH] video: fbdev: arkfb: Fix a divide-by-zero bug in ark_set_pixclock() Since the user can control the arguments of the ioctl() from the user space, under special arguments that may result in a divide-by-zero bug in: drivers/video/fbdev/arkfb.c:784: ark_set_pixclock(info, (hdiv * info->var.pixclock) / hmul); with hdiv=1, pixclock=1 and hmul=2 you end up with (1*1)/2 = (int) 0. and then in: drivers/video/fbdev/arkfb.c:504: rv = dac_set_freq(par->dac, 0, 1000000000 / pixclock); we'll get a division-by-zero. The following log can reveal it: divide error: 0000 [#1] PREEMPT SMP KASAN PTI RIP: 0010:ark_set_pixclock drivers/video/fbdev/arkfb.c:504 [inline] RIP: 0010:arkfb_set_par+0x10fc/0x24c0 drivers/video/fbdev/arkfb.c:784 Call Trace: fb_set_var+0x604/0xeb0 drivers/video/fbdev/core/fbmem.c:1034 do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1110 fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1189 Fix this by checking the argument of ark_set_pixclock() first. Fixes: dbd58d3aadcf ("arkfb: new framebuffer driver for ARK Logic cards") Signed-off-by: Zheyu Ma Signed-off-by: Helge Deller --- drivers/video/fbdev/arkfb.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/video/fbdev/arkfb.c b/drivers/video/fbdev/arkfb.c index eb3e47c58c5f7..ed76ddc7df3d1 100644 --- a/drivers/video/fbdev/arkfb.c +++ b/drivers/video/fbdev/arkfb.c @@ -781,7 +781,12 @@ static int arkfb_set_par(struct fb_info *info) return -EINVAL; } - ark_set_pixclock(info, (hdiv * info->var.pixclock) / hmul); + value = (hdiv * info->var.pixclock) / hmul; + if (!value) { + fb_dbg(info, "invalid pixclock\n"); + value = 1; + } + ark_set_pixclock(info, value); svga_set_timings(par->state.vgabase, &ark_timing_regs, &(info->var), hmul, hdiv, (info->var.vmode & FB_VMODE_DOUBLE) ? 2 : 1, (info->var.vmode & FB_VMODE_INTERLACED) ? 2 : 1, -- 2.39.5