[Xen-changelog] [qemu-xen-4.2-testing] pcnet: force the buffer access to be in bounds during tx

[patchbot@xxxxxxx]

commit 2b5c19892fd76d1c5b6b2a0b4fee6a35513b4999
Author:     Petr Matousek <pmatouse@xxxxxxxxxx>
AuthorDate: Sun May 24 10:53:44 2015 +0200
Commit:     Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CommitDate: Tue Jun 23 11:43:59 2015 +0100

    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 <pmatouse@xxxxxxxxxx>
    Reported-by: Matt Tait <matttait@xxxxxxxxxx>
    Reviewed-by: Peter Maydell <peter.maydell@xxxxxxxxxx>
    Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
---
 hw/pcnet.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/hw/pcnet.c b/hw/pcnet.c
index 9f3e1cc..4e81267 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;
--
generated by git-patchbot for /home/xen/git/qemu-xen-4.2-testing.git

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