[Qemu-devel] [PATCH 10/23] stellaris_enet: avoid buffer overrun on incoming migration

["Michael S. Tsirkin" <mst@redhat.com>]

From: Michael Roth <mdroth@linux.vnet.ibm.com>

CVE-2013-4532

s->next_packet is read from wire as an index into s->rx[]. If
s->next_packet exceeds the length of s->rx[], the buffer can be
subsequently overrun with arbitrary data from the wire.

Fix this by introducing a constant that defines the length of
s->rx[], and fail migration if the s->next_packet we read from
the wire exceeds this.

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/net/stellaris_enet.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/hw/net/stellaris_enet.c b/hw/net/stellaris_enet.c
index 9dd77f7..db12a99 100644
--- a/hw/net/stellaris_enet.c
+++ b/hw/net/stellaris_enet.c
@@ -61,13 +61,14 @@ typedef struct {
     uint32_t np;
     int tx_frame_len;
     int tx_fifo_len;
-    uint8_t tx_fifo[2048];
     /* Real hardware has a 2k fifo, which works out to be at most 31 packets.
        We implement a full 31 packet fifo.  */
+    uint8_t tx_fifo[2048];
+#define SE_RX_BUF_LEN 31
     struct {
         uint8_t data[2048];
         int len;
-    } rx[31];
+    } rx[SE_RX_BUF_LEN];
     uint8_t *rx_fifo;
     int rx_fifo_len;
     int next_packet;
@@ -92,15 +93,15 @@ static ssize_t stellaris_enet_receive(NetClientState *nc, const uint8_t *buf, si
 
     if ((s->rctl & SE_RCTL_RXEN) == 0)
         return -1;
-    if (s->np >= 31) {
+    if (s->np >= SE_RX_BUF_LEN) {
         DPRINTF("Packet dropped\n");
         return -1;
     }
 
     DPRINTF("Received packet len=%d\n", size);
     n = s->next_packet + s->np;
-    if (n >= 31)
-        n -= 31;
+    if (n >= SE_RX_BUF_LEN)
+        n -= SE_RX_BUF_LEN;
     s->np++;
 
     s->rx[n].len = size + 6;
@@ -132,7 +133,7 @@ static int stellaris_enet_can_receive(NetClientState *nc)
     if ((s->rctl & SE_RCTL_RXEN) == 0)
         return 1;
 
-    return (s->np < 31);
+    return (s->np < SE_RX_BUF_LEN);
 }
 
 static uint64_t stellaris_enet_read(void *opaque, hwaddr offset,
@@ -168,7 +169,7 @@ static uint64_t stellaris_enet_read(void *opaque, hwaddr offset,
         if (s->rx_fifo_len <= 0) {
             s->rx_fifo_len = 0;
             s->next_packet++;
-            if (s->next_packet >= 31)
+            if (s->next_packet >= SE_RX_BUF_LEN)
                 s->next_packet = 0;
             s->np--;
             DPRINTF("RX done np=%d\n", s->np);
@@ -344,7 +345,7 @@ static void stellaris_enet_save(QEMUFile *f, void *opaque)
     qemu_put_be32(f, s->tx_frame_len);
     qemu_put_be32(f, s->tx_fifo_len);
     qemu_put_buffer(f, s->tx_fifo, sizeof(s->tx_fifo));
-    for (i = 0; i < 31; i++) {
+    for (i = 0; i < SE_RX_BUF_LEN; i++) {
         qemu_put_be32(f, s->rx[i].len);
         qemu_put_buffer(f, s->rx[i].data, sizeof(s->rx[i].data));
 
@@ -375,12 +376,15 @@ static int stellaris_enet_load(QEMUFile *f, void *opaque, int version_id)
     s->tx_frame_len = qemu_get_be32(f);
     s->tx_fifo_len = qemu_get_be32(f);
     qemu_get_buffer(f, s->tx_fifo, sizeof(s->tx_fifo));
-    for (i = 0; i < 31; i++) {
+    for (i = 0; i < SE_RX_BUF_LEN; i++) {
         s->rx[i].len = qemu_get_be32(f);
         qemu_get_buffer(f, s->rx[i].data, sizeof(s->rx[i].data));
 
     }
     s->next_packet = qemu_get_be32(f);
+    if (s->next_packet >= SE_RX_BUF_LEN) {
+        return -EINVAL;
+    }
     s->rx_fifo = s->rx[s->next_packet].data + qemu_get_be32(f);
     s->rx_fifo_len = qemu_get_be32(f);
 
-- 
MST