Commit 6e157a03 authored by Fam Zheng's avatar Fam Zheng Committed by Samuel Thibault
Browse files

slirp: Add sanity check for str option length 



When user provides a long domainname or hostname that doesn't fit in the
DHCP packet, we mustn't overflow the response packet buffer. Instead,
report errors, following the g_warning() in the slirp->vdnssearch
branch.

Also check the strlen against 256 when initializing slirp, which limit
is also from the protocol where one byte represents the string length.
This gives an early error before the warning which is harder to notice
or diagnose.

Reported-by: default avatarThomas Huth <thuth@redhat.com>
Reviewed-by: default avatarThomas Huth <thuth@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: default avatarFam Zheng <famz@redhat.com>
Tested-by: default avatarGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: default avatarSamuel Thibault <samuel.thibault@ens-lyon.org>
parent b312532f

net/slirp.c

+9 −0
Original line number Diff line number Diff line
@@ -350,6 +350,15 @@ static int net_slirp_init(NetClientState *peer, const char *model, 
        return -1;

    }



    if (vdomainname && strlen(vdomainname) > 255) {

        error_setg(errp, "'domainname' parameter cannot exceed 255 bytes");

        return -1;

    }



    if (vhostname && strlen(vhostname) > 255) {

        error_setg(errp, "'vhostname' parameter cannot exceed 255 bytes");

        return -1;

    }



    nc = qemu_new_net_client(&net_slirp_info, peer, model, name);

slirp/bootp.c

+22 −10
Original line number Diff line number Diff line
@@ -159,6 +159,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t *bp) 
    struct in_addr preq_addr;

    int dhcp_msg_type, val;

    uint8_t *q;

    uint8_t *end;

    uint8_t client_ethaddr[ETH_ALEN];



    /* extract exact DHCP msg type */
@@ -240,6 +241,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t *bp) 
    rbp->bp_siaddr = saddr.sin_addr; /* Server IP address */



    q = rbp->bp_vend;

    end = (uint8_t *)&rbp[1];

    memcpy(q, rfc1533_cookie, 4);

    q += 4;
@@ -292,24 +294,33 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t *bp) 


        if (*slirp->client_hostname) {

            val = strlen(slirp->client_hostname);

            if (q + val + 2 >= end) {

                g_warning("DHCP packet size exceeded, "

                    "omitting host name option.");

            } else {

                *q++ = RFC1533_HOSTNAME;

                *q++ = val;

                memcpy(q, slirp->client_hostname, val);

                q += val;

            }

        }



        if (slirp->vdomainname) {

            val = strlen(slirp->vdomainname);

            if (q + val + 2 >= end) {

                g_warning("DHCP packet size exceeded, "

                    "omitting domain name option.");

            } else {

                *q++ = RFC1533_DOMAINNAME;

                *q++ = val;

                memcpy(q, slirp->vdomainname, val);

                q += val;

            }

        }



        if (slirp->vdnssearch) {

            size_t spaceleft = sizeof(rbp->bp_vend) - (q - rbp->bp_vend);

            val = slirp->vdnssearch_len;

            if (val + 1 > spaceleft) {

            if (q + val >= end) {

                g_warning("DHCP packet size exceeded, "

                    "omitting domain-search option.");

            } else {
@@ -331,6 +342,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t *bp) 
        memcpy(q, nak_msg, sizeof(nak_msg) - 1);

        q += sizeof(nak_msg) - 1;

    }

    assert(q < end);

    *q = RFC1533_END;



    daddr.sin_addr.s_addr = 0xffffffffu;