On 1/13/20 1:49 PM, Arnd Bergmann wrote: > On Fri, Jan 3, 2020 at 2:09 PM Bartlomiej Zolnierkiewicz > <b.zolnierkie@xxxxxxxxxxx> wrote: >> On 10/29/19 8:02 PM, Eric W. Biederman wrote: >>> >>> The goal is to avoid memory that has values of the previous users of >>> that memory region from leaking to userspace. Which depending on who >>> the previous user of that memory region is could tell userspace >>> information about what the kernel is doing that it should not be allowed >>> to find out. >>> >>> I tried to trace through where "info" and thus presumably "info->fix" is >>> coming from and only made it as far as register_framebuffer. Given >> >> "info" (and thus "info->fix") comes from framebuffer_alloc() (which is >> called by fbdev device drivers prior to registering "info" with >> register_framebuffer()). framebuffer_alloc() does kzalloc() on "info". >> >> Therefore shouldn't memcpy() (as suggested by Jeo Perches) be enough? > > Is it guaranteed that all drivers call framebuffer_alloc() rather than > open-coding it somewhere? > > Here is a list of all files that call register_framebuffer() without first > calling framebuffer_alloc: > > $ git grep -wl register_framebuffer | xargs grep -L framebuffer_alloc > Documentation/fb/framebuffer.rst > drivers/media/pci/ivtv/ivtvfb.c > drivers/media/platform/vivid/vivid-osd.c > drivers/video/fbdev/68328fb.c > drivers/video/fbdev/acornfb.c > drivers/video/fbdev/amba-clcd.c > drivers/video/fbdev/atafb.c > drivers/video/fbdev/au1100fb.c > drivers/video/fbdev/controlfb.c > drivers/video/fbdev/core/fbmem.c > drivers/video/fbdev/cyber2000fb.c > drivers/video/fbdev/fsl-diu-fb.c > drivers/video/fbdev/g364fb.c > drivers/video/fbdev/goldfishfb.c > drivers/video/fbdev/hpfb.c > drivers/video/fbdev/macfb.c > drivers/video/fbdev/matrox/matroxfb_base.c > drivers/video/fbdev/matrox/matroxfb_crtc2.c > drivers/video/fbdev/maxinefb.c > drivers/video/fbdev/ocfb.c > drivers/video/fbdev/pxafb.c > drivers/video/fbdev/sa1100fb.c > drivers/video/fbdev/stifb.c > drivers/video/fbdev/valkyriefb.c > drivers/video/fbdev/vermilion/vermilion.c > drivers/video/fbdev/vt8500lcdfb.c > drivers/video/fbdev/wm8505fb.c > drivers/video/fbdev/xilinxfb.c > > It's possible (even likely, the ones I looked at are fine) that they > all correctly > zero out the fb_info structure first, but it seems hard to guarantee, so > Eric's suggestion would possibly still be the safer choice. I've audited all above instances and they are all fine. They either use the fb_info structure embedded in a driver specific structure (which is zeroed out) or (in case of some m68k specific drivers) use a static fb_info instance. Since fbdev is closed for new drivers it should be now fine to use the simpler approach (just use memcpy()). Best regards, -- Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics
