Re: [PATCH] tty: vt: initialize unicode screen buffer

[Jiri Slaby]

On 19. 07. 22, 7:49, Tetsuo Handa wrote:
> 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]
> Reported-by: syzbot <syzbot+31a641689d43387f05d3@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

Yes, it makes sense.

Reviewed-by: Jiri Slaby <jirislaby@xxxxxxxxxx>

> ---
>   drivers/tty/vt/vt.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index f8c87c4d7399..6968517d6f8b 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -344,7 +344,7 @@ static struct uni_screen *vc_uniscr_alloc(unsigned int cols, unsigned int rows)
>   	/* 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;
>   

thanks,
--
js
suse labs