remote: Fix integer overflow in RPC handler for virNodeGetFreePages (CVE-2026-18917)

CVE-2026-18917

The RPC handler 'remoteDispatchNodeGetFreePages' multiplies the 'npages'
argument with the 'cellcount' argument passed to 'virNodeGetFreePages',
both of which are declared as 'unsigned int' to both do an RPC limit
check against the 'REMOTE_NODE_MAX_CELLS' constant and then to allocate
the memory to hold the result from the actual hypervisor driver.

Since both the values are 'unsigned int' the product is also unsigned
int so big enough numbers can overflow, both passing the check and also
allocating not enough memory for the result. The hypervisor driver
assumes that the passed buffer is large enough and overwrites memory.

When this happens the the hypervisor daemon crashes.

This can be triggered e.g. by passing 1023 and 4198405 as values which
multiply to 1019 after wrapping to 32 bit unsigned value.

Use the VIR_INT_MULTIPLY_OVERFLOW macro in the check to avoid the issue
the same way as we do for other APIs doing multiplication of arguments
to determine amount of required memory.

Fixes: 34f2d0319d (v1.2.5-164-g34f2d0319d)
Closes: https://gitlab.com/libvirt/libvirt/-/work_items/903
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

src/remote/remote_daemon_dispatch.c

@@ -6752,13 +6752,14 @@ remoteDispatchNodeGetFreePages(virNetServer *server G_GNUC_UNUSED,
     if (!conn)
         goto cleanup;
 
-    if (args->pages.pages_len * args->cellCount > REMOTE_NODE_MAX_CELLS) {
-        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                       _("the result won't fit into REMOTE_NODE_MAX_CELLS"));
+    if (VIR_INT_MULTIPLY_OVERFLOW(args->pages.pages_len, args->cellCount) ||
+        args->pages.pages_len * args->cellCount > REMOTE_NODE_MAX_CELLS) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("npages * cellcount > REMOTE_NODE_MAX_CELLS (%1$u)"),
+                       REMOTE_NODE_MAX_CELLS);
         goto cleanup;
     }
 
-    /* Allocate return buffer. */
     ret->counts.counts_val = g_new0(uint64_t,
                                     args->pages.pages_len * args->cellCount);