ProcDbeAllocateBackBufferName(ClientPtr client)
{
    REQUEST(xDbeAllocateBackBufferNameReq);
    WindowPtr pWin;
    DbeScreenPrivPtr pDbeScreenPriv;
    DbeWindowPrivPtr pDbeWindowPriv;
    XdbeScreenVisualInfo scrVisInfo;
    register int i;
    Bool visualMatched = FALSE;
    xDbeSwapAction swapAction;
    VisualID visual;
    int status;
    int add_index;

    REQUEST_SIZE_MATCH(xDbeAllocateBackBufferNameReq);

    /* The window must be valid. */
    status = dixLookupWindow(&pWin, stuff->window, client, DixManageAccess);
    if (status != Success)
        return status;

    /* The window must be InputOutput. */
    if (pWin->drawable.class != InputOutput) {
        return BadMatch;
    }

    /* The swap action must be valid. */
    swapAction = stuff->swapAction;     /* use local var for performance. */
    if ((swapAction != XdbeUndefined) &&
        (swapAction != XdbeBackground) &&
        (swapAction != XdbeUntouched) && (swapAction != XdbeCopied)) {
        return BadValue;
    }

    /* The id must be in range and not already in use. */
    LEGAL_NEW_RESOURCE(stuff->buffer, client);

    /* The visual of the window must be in the list returned by
     * GetVisualInfo.
     */
    pDbeScreenPriv = DBE_SCREEN_PRIV_FROM_WINDOW(pWin);
    if (!pDbeScreenPriv->GetVisualInfo)
        return BadMatch;        /* screen doesn't support double buffering */

    if (!(*pDbeScreenPriv->GetVisualInfo) (pWin->drawable.pScreen, &scrVisInfo)) {
        /* GetVisualInfo() failed to allocate visual info data. */
        return BadAlloc;
    }

    /* See if the window's visual is on the list. */
    visual = wVisual(pWin);
    for (i = 0; (i < scrVisInfo.count) && !visualMatched; i++) {
        if (scrVisInfo.visinfo[i].visual == visual) {
            visualMatched = TRUE;
        }
    }

    /* Free what was allocated by the GetVisualInfo() call above. */
    free(scrVisInfo.visinfo);

    if (!visualMatched) {
        return BadMatch;
    }

    if ((pDbeWindowPriv = DBE_WINDOW_PRIV(pWin)) == NULL) {
        /* There is no buffer associated with the window.
         * Allocate a window priv.
         */

        pDbeWindowPriv = calloc(1, sizeof(DbeWindowPrivRec));
        if (!pDbeWindowPriv)
            return BadAlloc;

        /* Fill out window priv information. */
        pDbeWindowPriv->pWindow = pWin;
        pDbeWindowPriv->width = pWin->drawable.width;
        pDbeWindowPriv->height = pWin->drawable.height;
        pDbeWindowPriv->x = pWin->drawable.x;
        pDbeWindowPriv->y = pWin->drawable.y;
        pDbeWindowPriv->nBufferIDs = 0;

        /* Set the buffer ID array pointer to the initial (static) array). */
        pDbeWindowPriv->IDs = pDbeWindowPriv->initIDs;

        /* Initialize the buffer ID list. */
        pDbeWindowPriv->maxAvailableIDs = DBE_INIT_MAX_IDS;
        pDbeWindowPriv->IDs[0] = stuff->buffer;

        add_index = 0;
        for (i = 0; i < DBE_INIT_MAX_IDS; i++) {
            pDbeWindowPriv->IDs[i] = DBE_FREE_ID_ELEMENT;
        }

        /* Actually connect the window priv to the window. */
        dixSetPrivate(&pWin->devPrivates, dbeWindowPrivKey, pDbeWindowPriv);

    }                           /* if -- There is no buffer associated with the window. */

    else {
        /* A buffer is already associated with the window.
         * Add the new buffer ID to the array, reallocating the array memory
         * if necessary.
         */

        /* Determine if there is a free element in the ID array. */
        for (i = 0; i < pDbeWindowPriv->maxAvailableIDs; i++) {
            if (pDbeWindowPriv->IDs[i] == DBE_FREE_ID_ELEMENT) {
                /* There is still room in the ID array. */
                break;
            }
        }

        if (i == pDbeWindowPriv->maxAvailableIDs) {
            /* No more room in the ID array -- reallocate another array. */
            XID *pIDs;

            /* Setup an array pointer for the realloc operation below. */
            if (pDbeWindowPriv->maxAvailableIDs == DBE_INIT_MAX_IDS) {
                /* We will malloc a new array. */
                pIDs = NULL;
            }
            else {
                /* We will realloc a new array. */
                pIDs = pDbeWindowPriv->IDs;
            }

            /* malloc/realloc a new array and initialize all elements to 0. */
            pDbeWindowPriv->IDs =
                reallocarray(pIDs,
                             pDbeWindowPriv->maxAvailableIDs + DBE_INCR_MAX_IDS,
                             sizeof(XID));
            if (!pDbeWindowPriv->IDs) {
                return BadAlloc;
            }
            memset(&pDbeWindowPriv->IDs[pDbeWindowPriv->nBufferIDs], 0,
                   (pDbeWindowPriv->maxAvailableIDs + DBE_INCR_MAX_IDS -
                    pDbeWindowPriv->nBufferIDs) * sizeof(XID));

            if (pDbeWindowPriv->maxAvailableIDs == DBE_INIT_MAX_IDS) {
                /* We just went from using the initial (static) array to a
                 * newly allocated array.  Copy the IDs from the initial array
                 * to the new array.
                 */
                memcpy(pDbeWindowPriv->IDs, pDbeWindowPriv->initIDs,
                       DBE_INIT_MAX_IDS * sizeof(XID));
            }

            pDbeWindowPriv->maxAvailableIDs += DBE_INCR_MAX_IDS;
        }

        add_index = i;

    }                           /* else -- A buffer is already associated with the window. */

    /* Call the DDX routine to allocate the back buffer. */
    status = (*pDbeScreenPriv->AllocBackBufferName) (pWin, stuff->buffer,
                                                     stuff->swapAction);

    if (status == Success) {
        pDbeWindowPriv->IDs[add_index] = stuff->buffer;
        if (!AddResource(stuff->buffer, dbeWindowPrivResType,
                         (void *) pDbeWindowPriv)) {
            pDbeWindowPriv->IDs[add_index] = DBE_FREE_ID_ELEMENT;

            if (pDbeWindowPriv->nBufferIDs == 0) {
                status = BadAlloc;
                goto out_free;
            }
        }
    }
    else {
        /* The DDX buffer allocation routine failed for the first buffer of
         * this window.
         */
        if (pDbeWindowPriv->nBufferIDs == 0) {
            goto out_free;
        }
    }

    /* Increment the number of buffers (XIDs) associated with this window. */
    pDbeWindowPriv->nBufferIDs++;

    /* Set swap action on all calls. */
    pDbeWindowPriv->swapAction = stuff->swapAction;

    return status;

 out_free:
    dixSetPrivate(&pWin->devPrivates, dbeWindowPrivKey, NULL);
    free(pDbeWindowPriv);
    return status;

}                               /* ProcDbeAllocateBackBufferName() */

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.