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    Subject[PATCH 5.4 022/389] tty: vt: initialize unicode screen buffer
    Date
    From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

    commit af77c56aa35325daa2bc2bed5c2ebf169be61b86 upstream.

    syzbot reports kernel infoleak at vcs_read() [1], for buffer can be read
    immediately after resize operation. Initialize buffer using kzalloc().

    ----------
    #include <fcntl.h>
    #include <unistd.h>
    #include <sys/ioctl.h>
    #include <linux/fb.h>

    int main(int argc, char *argv[])
    {
    struct fb_var_screeninfo var = { };
    const int fb_fd = open("/dev/fb0", 3);
    ioctl(fb_fd, FBIOGET_VSCREENINFO, &var);
    var.yres = 0x21;
    ioctl(fb_fd, FBIOPUT_VSCREENINFO, &var);
    return read(open("/dev/vcsu", O_RDONLY), &var, sizeof(var)) == -1;
    }
    ----------

    Link: https://syzkaller.appspot.com/bug?extid=31a641689d43387f05d3 [1]
    Cc: stable <stable@vger.kernel.org>
    Reported-by: syzbot <syzbot+31a641689d43387f05d3@syzkaller.appspotmail.com>
    Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
    Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Link: https://lore.kernel.org/r/4ef053cf-e796-fb5e-58b7-3ae58242a4ad@I-love.SAKURA.ne.jp
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/tty/vt/vt.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/tty/vt/vt.c
    +++ b/drivers/tty/vt/vt.c
    @@ -351,7 +351,7 @@ static struct uni_screen *vc_uniscr_allo
    /* allocate everything in one go */
    memsize = cols * rows * sizeof(char32_t);
    memsize += rows * sizeof(char32_t *);
    - p = vmalloc(memsize);
    + p = vzalloc(memsize);
    if (!p)
    return NULL;


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