net: pcnet: add check to validate receive data size(CVE-2015-7504) In loopback mode, pcnet_receive routine appends CRC code to the receive buffer. If the data size given is same as the buffer size, the appended CRC code overwrites 4 bytes after s->buffer. Added a check to avoid that. Reported-by: Qinghao Tang <luodalongde@gmail.com> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org> --- tools/qemu-xen-traditional/hw/net/pcnet.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/tools/qemu-xen-traditional/hw/pcnet.c b/tools/qemu-xen-traditional/hw/pcnet.c index 4e81267..6a101f2 100644 --- a/tools/qemu-xen-traditional/hw/pcnet.c +++ b/tools/qemu-xen-traditional/hw/pcnet.c @@ -1153,7 +1153,7 @@ static void pcnet_receive(void *opaque, const uint8_t *buf, int size) uint32_t fcs = ~0; uint8_t *p = src; - while (p != &src[size-4]) + while (p != &src[size]) CRC(fcs, *p++); crc_err = (*(uint32_t *)p != htonl(fcs)); } @@ -1284,12 +1284,13 @@ static void pcnet_transmit(PCNetState *s) bcnt = 4096 - GET_FIELD(tmd.length, TMDL, BCNT); /* if multi-tmd packet outsizes s->buffer then skip it silently. - Note: this is not what real hw does */ - if (s->xmit_pos + bcnt > sizeof(s->buffer)) { - s->xmit_pos = -1; - goto txdone; + * Note: this is not what real hw does. + * Last four bytes of s->buffer are used to store CRC FCS code. + */ + if (s->xmit_pos + bcnt > sizeof(s->buffer) - 4) { + s->xmit_pos = -1; + goto txdone; } - s->phys_mem_read(s->dma_opaque, PHYSADDR(s, tmd.tbadr), s->buffer + s->xmit_pos, bcnt, CSR_BSWP(s)); s->xmit_pos += bcnt; --- -2.4.3 -