Re: [Qemu-stable] [Qemu-devel] [PATCH] slirp: check sscanf result when emulating ident

[William Bowling]

Hi Phil,

William: How did you notice that? Using a static analyzer?

It was while looking into a previous CVE in tcp_emu, just with a manual code review. 

We have a data leak, Cc'ing qemu-stable.
(Adding the address I noticed you Cc'ed address@hidden, so that
confirms my guess).

Yeah the report and patch went via the security list initially due to the info leak.

Cheers,

Will

On Sun, Mar 3, 2019 at 4:42 AM Philippe Mathieu-Daudé <address@hidden> wrote:

Hi William, Samuel,

On 3/1/19 10:45 PM, William Bowling wrote:
> When emulating ident in tcp_emu, if the strchr checks passed but the
> sscanf check failed, two uninitialized variables would be copied and
> sent in the reply.

William: How did you notice that? Using a static analyzer?

Samuel: since this diff is not obvious without looking at the context
(also due to the code re-indent), can you improve the commit
description, such (or better):

"Move this code inside the if(sscanf()) clause".

We have a data leak, Cc'ing qemu-stable.
(Adding the address I noticed you Cc'ed address@hidden, so that
confirms my guess).

>
> Signed-off-by: William Bowling <address@hidden>

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

Thanks,

Phil.

> ---
>  slirp/tcp_subr.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
> index 262a42d6c8..73a160ba16 100644
> --- a/slirp/tcp_subr.c
> +++ b/slirp/tcp_subr.c
> @@ -664,12 +664,12 @@ tcp_emu(struct socket *so, struct mbuf *m)
>                                                       break;
>                                               }
>                                       }
> -                             }
> -                                so_rcv->sb_cc = snprintf(so_rcv->sb_data,
> -                                                         so_rcv->sb_datalen,
> -                                                         "%d,%d\r\n", n1, n2);
> -                             so_rcv->sb_rptr = so_rcv->sb_data;
> -                             so_rcv->sb_wptr = so_rcv->sb_data + so_rcv->sb_cc;
> +                    so_rcv->sb_cc = snprintf(so_rcv->sb_data,
> +                                             so_rcv->sb_datalen,
> +                                             "%d,%d\r\n", n1, n2);
> +                    so_rcv->sb_rptr = so_rcv->sb_data;
> +                    so_rcv->sb_wptr = so_rcv->sb_data + so_rcv->sb_cc;
> +                }
>                       }
>                       m_free(m);
>                       return 0;
>

--

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