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    Subject[PATCH 5.10 432/545] video: fbdev: arkfb: Fix a divide-by-zero bug in ark_set_pixclock()
    Date
    From: Zheyu Ma <zheyuma97@gmail.com>

    [ Upstream commit 2f1c4523f7a3aaabe7e53d3ebd378292947e95c8 ]

    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: 681e14730c73 ("arkfb: new framebuffer driver for ARK Logic cards")
    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/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 edf169d0816e..d94cc5ad1ef6 100644
    --- a/drivers/video/fbdev/arkfb.c
    +++ b/drivers/video/fbdev/arkfb.c
    @@ -778,7 +778,12 @@ 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,
    --
    2.35.1


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