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@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 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;
 
-- 
2.34.1

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@syzkaller.appspotmail.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

Yes, it makes sense.

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>

> ---
>   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