Messages in this thread | | | Date | Fri, 25 Jul 2003 01:04:48 +0100 (BST) | From | James Simmons <> | Subject | Re: How is info->cmap supposed to work? |
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> Hi James, > I have few problems with understanding how > info->cmap is supposed to work:
Hi!
> (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.
I think I posted something about that some time ago and I didn't here anything. Looking at the code I realized that yeap its broke. Its strange that both fb_set_cmap and fb_copy_cmap can get data from userland. I would think that we either have fb_set_cmap just set the video hardware or have fb_set_cmap be able to grab data from userland and fb_copy_cmap send data to userland.
> (2) FBIOPUTCMAP calls fb_set_cmap, which in turn calls > fb_setcolreg.
True.
> FBIOGETCMAP copies cmap entries from > info->cmap (after fixing (1)). Does it mean that > fb_setcolreg has to fill info->cmap itself?
No. At present all the drivers initialize a default cmap. Then it doesn't matter which function gets called first.
> 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.
:-( I have to look to see if that has been around for a while. I have a feeling it has been.
> (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?
The reason for the driver initalizing the default cmap is because we don't know how big the actual colormap will be. I don't know if the generic method of setting to color map to 2^bpp until above 8 bpp mode in which case we only set 16 colors will always work. Perhaps we could just set the cmap.len field and have the upper layer just generate from that.
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