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    Subject[PATCH 5.10 035/545] fbcon: Fix boundary checks for fbcon=vc:n1-n2 parameters
    Date
    From: Helge Deller <deller@gmx.de>

    commit cad564ca557f8d3bb3b1fa965d9a2b3f6490ec69 upstream.

    The user may use the fbcon=vc:<n1>-<n2> option to tell fbcon to take
    over the given range (n1...n2) of consoles. The value for n1 and n2
    needs to be a positive number and up to (MAX_NR_CONSOLES - 1).
    The given values were not fully checked against those boundaries yet.

    To fix the issue, convert first_fb_vc and last_fb_vc to unsigned
    integers and check them against the upper boundary, and make sure that
    first_fb_vc is smaller than last_fb_vc.

    Cc: stable@vger.kernel.org # v4.19+
    Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    Signed-off-by: Helge Deller <deller@gmx.de>
    Link: https://patchwork.freedesktop.org/patch/msgid/YpkYRMojilrtZIgM@p100
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/video/fbdev/core/fbcon.c | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    --- a/drivers/video/fbdev/core/fbcon.c
    +++ b/drivers/video/fbdev/core/fbcon.c
    @@ -123,8 +123,8 @@ static int logo_lines;
    enums. */
    static int logo_shown = FBCON_LOGO_CANSHOW;
    /* console mappings */
    -static int first_fb_vc;
    -static int last_fb_vc = MAX_NR_CONSOLES - 1;
    +static unsigned int first_fb_vc;
    +static unsigned int last_fb_vc = MAX_NR_CONSOLES - 1;
    static int fbcon_is_default = 1;
    static int primary_device = -1;
    static int fbcon_has_console_bind;
    @@ -472,10 +472,12 @@ static int __init fb_console_setup(char
    options += 3;
    if (*options)
    first_fb_vc = simple_strtoul(options, &options, 10) - 1;
    - if (first_fb_vc < 0)
    + if (first_fb_vc >= MAX_NR_CONSOLES)
    first_fb_vc = 0;
    if (*options++ == '-')
    last_fb_vc = simple_strtoul(options, &options, 10) - 1;
    + if (last_fb_vc < first_fb_vc || last_fb_vc >= MAX_NR_CONSOLES)
    + last_fb_vc = MAX_NR_CONSOLES - 1;
    fbcon_is_default = 0;
    continue;
    }

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