Re: [Qemu-devel] [PATCH] net: rocker: fix an incorrect array bounds check

[P J P <ppandit@redhat.com>]

+-- On Tue, 22 Dec 2015, Paolo Bonzini wrote --+
| > -        if (++iovcnt > ROCKER_TX_FRAGS_MAX) {
| > +        if (++iovcnt >= ROCKER_TX_FRAGS_MAX) {
| 
| Doesn't this forbid some valid ROCKER_TX_FRAGS_MAX-element iovecs?

  forbid..?  Sorry, I did not get the question.

| The check should be moved before the assignment to iov[iovcnt].iov_len.

  You mean like below..?

===
diff --git a/hw/net/rocker/rocker.c b/hw/net/rocker/rocker.c
index c57f1a6..2e77e50 100644
--- a/hw/net/rocker/rocker.c
+++ b/hw/net/rocker/rocker.c
@@ -232,6 +232,9 @@ static int tx_consume(Rocker *r, DescInfo *info)
         frag_addr = rocker_tlv_get_le64(tlvs[ROCKER_TLV_TX_FRAG_ATTR_ADDR]);
         frag_len = rocker_tlv_get_le16(tlvs[ROCKER_TLV_TX_FRAG_ATTR_LEN]);
 
+        if (iovcnt >= ROCKER_TX_FRAGS_MAX) {
+            goto err_too_many_frags;
+        }
         iov[iovcnt].iov_len = frag_len;
         iov[iovcnt].iov_base = g_malloc(frag_len);
         if (!iov[iovcnt].iov_base) {
@@ -244,10 +247,7 @@ static int tx_consume(Rocker *r, DescInfo *info)
             err = -ROCKER_ENXIO;
             goto err_bad_io;
         }
-
-        if (++iovcnt > ROCKER_TX_FRAGS_MAX) {
-            goto err_too_many_frags;
-        }
+        iovcnt++;
     }
 
     if (iovcnt) {
===

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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