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>
---
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
-