From: Zheyu Ma zheyuma97@gmail.com
[ Upstream commit 40bf722f8064f50200b8c4f8946cd625b441dda9 ]
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.
If the user provides an improper 'pixclock' value that makes the argumet of i740_calc_vclk() less than 'I740_RFREQ_FIX', it will cause a divide-by-zero bug in: drivers/video/fbdev/i740fb.c:353 p_best = min(15, ilog2(I740_MAX_VCO_FREQ / (freq / I740_RFREQ_FIX)));
The following log can reveal it:
divide error: 0000 [#1] PREEMPT SMP KASAN PTI RIP: 0010:i740_calc_vclk drivers/video/fbdev/i740fb.c:353 [inline] RIP: 0010:i740fb_decode_var drivers/video/fbdev/i740fb.c:646 [inline] RIP: 0010:i740fb_set_par+0x163f/0x3b70 drivers/video/fbdev/i740fb.c:742 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 i740_calc_vclk() first.
Signed-off-by: Zheyu Ma zheyuma97@gmail.com Signed-off-by: Helge Deller deller@gmx.de Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/video/fbdev/i740fb.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/video/fbdev/i740fb.c b/drivers/video/fbdev/i740fb.c index 7bc5f6056c77..4147a9534179 100644 --- a/drivers/video/fbdev/i740fb.c +++ b/drivers/video/fbdev/i740fb.c @@ -399,7 +399,7 @@ static int i740fb_decode_var(const struct fb_var_screeninfo *var, u32 xres, right, hslen, left, xtotal; u32 yres, lower, vslen, upper, ytotal; u32 vxres, xoffset, vyres, yoffset; - u32 bpp, base, dacspeed24, mem; + u32 bpp, base, dacspeed24, mem, freq; u8 r7; int i;
@@ -641,7 +641,12 @@ static int i740fb_decode_var(const struct fb_var_screeninfo *var, par->atc[VGA_ATC_OVERSCAN] = 0;
/* Calculate VCLK that most closely matches the requested dot clock */ - i740_calc_vclk((((u32)1e9) / var->pixclock) * (u32)(1e3), par); + freq = (((u32)1e9) / var->pixclock) * (u32)(1e3); + if (freq < I740_RFREQ_FIX) { + fb_dbg(info, "invalid pixclock\n"); + freq = I740_RFREQ_FIX; + } + i740_calc_vclk(freq, par);
/* Since we program the clocks ourselves, always use VCLK2. */ par->misc |= 0x0C;