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 Signed-off-by: Prasad J Pandit --- hw/net/pcnet.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/hw/net/pcnet.c b/hw/net/pcnet.c index 3437376..5f55591 100644 --- a/hw/net/pcnet.c +++ b/hw/net/pcnet.c @@ -1085,7 +1085,7 @@ ssize_t pcnet_receive(NetClientState *nc, const uint8_t *buf, size_t 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)); } @@ -1234,8 +1234,10 @@ 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)) { + * 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; } -- 2.4.3