How is info->cmap supposed to work?

From: Petr Vandrovec (
Date: Mon Jul 21 2003 - 10:26:46 EST

Hi James,
  I have few problems with understanding how
info->cmap is supposed to work:

(1) FBIOGETCMAP calls fb_copy_cmap(&info->cmap, &cmap, 0);
    Should not it use last argument of '2', as &cmap points
    to the userspace? It looks to me like that anybody can
    overwrite kernel currently... Only positive side is that
    there is no way to control info->cmap contents (see (2)),
    so you can only crash kernel with random code, you cannot
    stuff some malicious code there.

(2) FBIOPUTCMAP calls fb_set_cmap, which in turn calls
    fb_setcolreg. FBIOGETCMAP copies cmap entries from
    info->cmap (after fixing (1)). Does it mean that
    fb_setcolreg has to fill info->cmap itself? Is not it
    a bit ugly? And fb_set_cmap documentation is incorrect:
    kspc == 0 means copy from userspace, while
    kspc != 0 means copy "local", inside kernel-space. Documentation
    says that 0 is local, while 1 is get_user.

(3) And who is supposed to initialize info->cmap, and to
    what value? It looks to me like that fbdev driver is
    supposed to do:

      memset(&info->cmap, 0, sizeof(info->cmap));
      fb_alloc_cmap(&info->cmap, 256, 1);

    Is it right? What about fb_init_cmap() then? And why
    fbdev has to play with info->cmap, cannot generic
    layer take a care of this, if all info->cmap accesses
    go through generic layer, and fbdev driver itself has
    no need for this field?

                                            Petr Vandrovec

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