From 91c15bfaec1764ce2896a393eabee1183afe1130 Mon Sep 17 00:00:00 2001 From: Ian Jackson Date: Wed, 9 Dec 2015 11:47:35 +0000 Subject: [PATCH] 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. This is XSA-162. Reported-by: Qinghao Tang Signed-off-by: Prasad J Pandit --- hw/pcnet.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/hw/pcnet.c b/hw/pcnet.c index 4e81267aec..6a101f229c 100644 --- a/hw/pcnet.c +++ b/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; -- 2.39.5