From: Petr Matousek Date: Sun, 24 May 2015 08:53:44 +0000 (+0200) Subject: pcnet: force the buffer access to be in bounds during tx X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;ds=sidebyside;p=qemu-xen-4.1-testing.git pcnet: force the buffer access to be in bounds during tx 4096 is the maximum length per TMD and it is also currently the size of the relay buffer pcnet driver uses for sending the packet data to QEMU for further processing. With packet spanning multiple TMDs it can happen that the overall packet size will be bigger than sizeof(buffer), which results in memory corruption. Fix this by only allowing to queue maximum sizeof(buffer) bytes. This is CVE-2015-3209. Signed-off-by: Petr Matousek Reported-by: Matt Tait Reviewed-by: Peter Maydell Reviewed-by: Stefan Hajnoczi --- diff --git a/hw/pcnet.c b/hw/pcnet.c index 9f3e1ccf2..4e81267ae 100644 --- a/hw/pcnet.c +++ b/hw/pcnet.c @@ -1282,6 +1282,14 @@ 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; + } + s->phys_mem_read(s->dma_opaque, PHYSADDR(s, tmd.tbadr), s->buffer + s->xmit_pos, bcnt, CSR_BSWP(s)); s->xmit_pos += bcnt;