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    Subject[PATCH 4.19 181/287] video: fbdev: vt8623fb: Check the size of screen before memset_io()
    Date
    From: Zheyu Ma <zheyuma97@gmail.com>

    [ Upstream commit ec0754c60217248fa77cc9005d66b2b55200ac06 ]

    In the function vt8623fb_set_par(), the value of 'screen_size' is
    calculated by the user input. If the user provides the improper value,
    the value of 'screen_size' may larger than 'info->screen_size', which
    may cause the following bug:

    [ 583.339036] BUG: unable to handle page fault for address: ffffc90005000000
    [ 583.339049] #PF: supervisor write access in kernel mode
    [ 583.339052] #PF: error_code(0x0002) - not-present page
    [ 583.339074] RIP: 0010:memset_orig+0x33/0xb0
    [ 583.339110] Call Trace:
    [ 583.339118] vt8623fb_set_par+0x11cd/0x21e0
    [ 583.339146] fb_set_var+0x604/0xeb0
    [ 583.339181] do_fb_ioctl+0x234/0x670
    [ 583.339209] fb_ioctl+0xdd/0x130

    Fix the this by checking the value of 'screen_size' before memset_io().

    Fixes: 558b7bd86c32 ("vt8623fb: new framebuffer driver for VIA VT8623")
    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/vt8623fb.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/drivers/video/fbdev/vt8623fb.c b/drivers/video/fbdev/vt8623fb.c
    index 5cac871db3ee..cbae9c510092 100644
    --- a/drivers/video/fbdev/vt8623fb.c
    +++ b/drivers/video/fbdev/vt8623fb.c
    @@ -504,6 +504,8 @@ static int vt8623fb_set_par(struct fb_info *info)
    (info->var.vmode & FB_VMODE_DOUBLE) ? 2 : 1, 1,
    1, info->node);

    + if (screen_size > info->screen_size)
    + screen_size = info->screen_size;
    memset_io(info->screen_base, 0x00, screen_size);

    /* Device and screen back on */
    --
    2.35.1


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