[Qemu-devel] [PATCH] slirp: check data length while emulating ident function

[Qemu-devel] [PATCH] slirp: check data length while emulating ident function

[P J P]

From: Prasad J Pandit <pjp@fedoraproject.org>

While emulating identification protocol, tcp_emu() does not check
available space in the 'sc_rcv->sb_data' buffer. It could lead to
heap buffer overflow issue. Add check to avoid it.

Reported-by: Kira <864786842@qq.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 slirp/tcp_subr.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
index fa61349cbb..4415801fbb 100644
--- a/slirp/tcp_subr.c
+++ b/slirp/tcp_subr.c
@@ -635,6 +635,11 @@ tcp_emu(struct socket *so, struct mbuf *m)
 			socklen_t addrlen = sizeof(struct sockaddr_in);
 			struct sbuf *so_rcv = &so->so_rcv;
 
+            if (m->m_len > so_rcv->sb_datalen
+                            - (so_rcv->sb_wptr - so_rcv->sb_data)) {
+                m_free(m);
+                return 0;
+            }
 			memcpy(so_rcv->sb_wptr, m->m_data, m->m_len);
 			so_rcv->sb_wptr += m->m_len;
 			so_rcv->sb_rptr += m->m_len;
-- 
2.20.1

Re: [Qemu-devel] [PATCH] slirp: check data length while emulating ident function

[Marc-André Lureau]

Hi

On Fri, Jan 11, 2019 at 12:31 PM P J P <ppandit@redhat.com> wrote:
>
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> While emulating identification protocol, tcp_emu() does not check
> available space in the 'sc_rcv->sb_data' buffer. It could lead to
> heap buffer overflow issue. Add check to avoid it.
>
> Reported-by: Kira <864786842@qq.com>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  slirp/tcp_subr.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
> index fa61349cbb..4415801fbb 100644
> --- a/slirp/tcp_subr.c
> +++ b/slirp/tcp_subr.c
> @@ -635,6 +635,11 @@ tcp_emu(struct socket *so, struct mbuf *m)
>                         socklen_t addrlen = sizeof(struct sockaddr_in);
>                         struct sbuf *so_rcv = &so->so_rcv;
>
> +            if (m->m_len > so_rcv->sb_datalen
> +                            - (so_rcv->sb_wptr - so_rcv->sb_data)) {
> +                m_free(m);
> +                return 0;
> +            }

Check looks correct, it should probably return 1.

Is there a reproducer?

>                         memcpy(so_rcv->sb_wptr, m->m_data, m->m_len);
>                         so_rcv->sb_wptr += m->m_len;
>                         so_rcv->sb_rptr += m->m_len;
> --
> 2.20.1
>
>


-- 
Marc-André Lureau

Re: [Qemu-devel] [PATCH] slirp: check data length while emulating ident function

[P J P]

+-- On Fri, 11 Jan 2019, Marc-André Lureau wrote --+
| > +            if (m->m_len > so_rcv->sb_datalen
| > +                            - (so_rcv->sb_wptr - so_rcv->sb_data)) {
| > +                m_free(m);
| > +                return 0;
| > +            }
| 
| Check looks correct, it should probably return 1.

Function comment says return 1 if 'm' is valid and should be appended via 
sbappend(). Not sure if unprocessed 'm' should go to sbappend().

| Is there a reproducer?

Yes, I have one.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F

Re: [Qemu-devel] [PATCH] slirp: check data length while emulating ident function

[Marc-André Lureau]

Hi

On Fri, Jan 11, 2019 at 1:18 PM P J P <ppandit@redhat.com> wrote:
>
> +-- On Fri, 11 Jan 2019, Marc-André Lureau wrote --+
> | > +            if (m->m_len > so_rcv->sb_datalen
> | > +                            - (so_rcv->sb_wptr - so_rcv->sb_data)) {
> | > +                m_free(m);
> | > +                return 0;
> | > +            }
> |
> | Check looks correct, it should probably return 1.
>
> Function comment says return 1 if 'm' is valid and should be appended via
> sbappend(). Not sure if unprocessed 'm' should go to sbappend().

If you look at the rest of the function, many similar error cases return 1.

> | Is there a reproducer?
>
> Yes, I have one.

Ok, could you add it to the commit message ? :)

>
> Thank you.
> --
> Prasad J Pandit / Red Hat Product Security Team
> 47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F



-- 
Marc-André Lureau

Re: [Qemu-devel] [PATCH] slirp: check data length while emulating ident function

[P J P]

+-- On Fri, 11 Jan 2019, Marc-André Lureau wrote --+
| > | Check looks correct, it should probably return 1.
| >
| > Function comment says return 1 if 'm' is valid and should be appended via
| > sbappend(). Not sure if unprocessed 'm' should go to sbappend().
| 
| If you look at the rest of the function, many similar error cases return 1.

True, not sure if that's right in this case. Nonetheless, I have sent a 
revised patch to return 1.
 
| Ok, could you add it to the commit message ? :)

No, I'm afraid not.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F