Re: [PATCH AUTOSEL 5.5 27/28] tty: fix compat TIOCGSERIAL leaking uninitialized memory

[Greg KH]

On Thu, Mar 26, 2020 at 07:23:56PM -0400, Sasha Levin wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
> 
> [ Upstream commit 17329563a97df3ba474eca5037c1336e46e14ff8 ]
> 
> Commit 77654350306a ("take compat TIOC[SG]SERIAL treatment into
> tty_compat_ioctl()") changed the compat version of TIOCGSERIAL to start
> copying a whole 'serial_struct32' to userspace rather than individual
> fields, but failed to initialize all padding and fields -- namely the
> hole after the 'iomem_reg_shift' field, and the 'reserved' field.
> 
> Fix this by initializing the struct to zero.
> 
> [v2: use sizeof, and convert the adjacent line for consistency.]
> 
> Reported-by: syzbot+8da9175e28eadcb203ce@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 77654350306a ("take compat TIOC[SG]SERIAL treatment into tty_compat_ioctl()")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.20+
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> Acked-by: Jiri Slaby <jslaby@xxxxxxx>
> Link: https://lore.kernel.org/r/20200224182044.234553-2-ebiggers@xxxxxxxxxx
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  drivers/tty/tty_io.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index d9f54c7d94f29..186e08a81b986 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -2734,7 +2734,9 @@ static int compat_tty_tiocgserial(struct tty_struct *tty,
>  	struct serial_struct32 v32;
>  	struct serial_struct v;
>  	int err;
> -	memset(&v, 0, sizeof(struct serial_struct));
> +
> +	memset(&v, 0, sizeof(v));
> +	memset(&v32, 0, sizeof(v32));
>  
>  	if (!tty->ops->set_serial)
>  		return -ENOTTY;
> -- 
> 2.20.1
> 

This is already in 5.4.28 and 5.5.12, so no need to add it again :)