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    Subject[PATCH 5.10 438/545] video: fbdev: s3fb: Check the size of screen before memset_io()
    Date
    From: Zheyu Ma <zheyuma97@gmail.com>

    [ Upstream commit 6ba592fa014f21f35a8ee8da4ca7b95a018f13e8 ]

    In the function s3fb_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:

    [ 54.083733] BUG: unable to handle page fault for address: ffffc90003000000
    [ 54.083742] #PF: supervisor write access in kernel mode
    [ 54.083744] #PF: error_code(0x0002) - not-present page
    [ 54.083760] RIP: 0010:memset_orig+0x33/0xb0
    [ 54.083782] Call Trace:
    [ 54.083788] s3fb_set_par+0x1ec6/0x4040
    [ 54.083806] fb_set_var+0x604/0xeb0
    [ 54.083836] do_fb_ioctl+0x234/0x670

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

    Fixes: a268422de8bf ("fbdev driver for S3 Trio/Virge")
    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/s3fb.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/drivers/video/fbdev/s3fb.c b/drivers/video/fbdev/s3fb.c
    index 5c74253e7b2c..a936455a3df2 100644
    --- a/drivers/video/fbdev/s3fb.c
    +++ b/drivers/video/fbdev/s3fb.c
    @@ -902,6 +902,8 @@ static int s3fb_set_par(struct fb_info *info)
    value = clamp((htotal + hsstart + 1) / 2 + 2, hsstart + 4, htotal + 1);
    svga_wcrt_multi(par->state.vgabase, s3_dtpc_regs, value);

    + if (screen_size > info->screen_size)
    + screen_size = info->screen_size;
    memset_io(info->screen_base, 0x00, screen_size);
    /* Device and screen back on */
    svga_wcrt_mask(par->state.vgabase, 0x17, 0x80, 0x80);
    --
    2.35.1


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