Bug 1973349 (CVE-2021-3607)

An integer overflow was found in the QEMU implementation of VMWare's paravirtual RDMA device. It could occur while handling a "PVRDMA_REG_DSRHIGH" write from the guest due to improper input validation. More specifically, the init_dev_ring() function in pvrdma_main.c does not validate the guest supplied 'num_pages' which is subsequently decremented and used in pvrdma_ring_init() to allocate dynamic memory via g_malloc(). This could result in a NULL pointer dereference issue (if g_malloc returns NULL) or allocation of large amount of memory and out-of-bounds read access. A privileged guest user could exploit this flaw to crash the QEMU process on the host, resulting in a denial of service condition.

static int init_dev_ring(..., uint32_t num_pages) {
  ...
  rc = pvrdma_ring_init(..., (dma_addr_t)num_pages - 1); // guest may provide num_pages = 0
  ...
}

int pvrdma_ring_init(..., uint32_t npages) {
  ...
  ring->pages = g_malloc(npages * sizeof(void *)); // npages may be -1 here
  for (i = 0; i < npages; i++) {
    ...
    ring->pages[i] = rdma_pci_dma_map(dev, tbl[i], TARGET_PAGE_SIZE);
  ...
}