From: Roman Penyaev rpenyaev@suse.de Subject: mm/vmalloc: fix size check for remap_vmalloc_range_partial()

When VM_NO_GUARD is not set area->size includes adjacent guard page, thus for correct size checking get_vm_area_size() should be used, but not area->size.

This fixes possible kernel oops when userspace tries to mmap an area on 1 page bigger than was allocated by vmalloc_user() call: the size check inside remap_vmalloc_range_partial() accounts non-existing guard page also, so check successfully passes but vmalloc_to_page() returns NULL (guard page does not physically exist).

The following code pattern example should trigger an oops:

static int oops_mmap(struct file *file, struct vm_area_struct *vma) { void *mem;

mem = vmalloc_user(4096); BUG_ON(!mem); /* Do not care about mem leak */

return remap_vmalloc_range(vma, mem, 0); }

And userspace simply mmaps size + PAGE_SIZE:

mmap(NULL, 8192, PROT_WRITE|PROT_READ, MAP_PRIVATE, fd, 0);

Possible candidates for oops which do not have any explicit size checks:

*** drivers/media/usb/stkwebcam/stk-webcam.c: v4l_stk_mmap[789] ret = remap_vmalloc_range(vma, sbuf->buffer, 0);

Or the following one:

*** drivers/video/fbdev/core/fbmem.c static int fb_mmap(struct file *file, struct vm_area_struct * vma) ... res = fb->fb_mmap(info, vma);

Where fb_mmap callback calls remap_vmalloc_range() directly without any explicit checks:

*** drivers/video/fbdev/vfb.c static int vfb_mmap(struct fb_info *info, struct vm_area_struct *vma) { return remap_vmalloc_range(vma, (void *)info->fix.smem_start, vma->vm_pgoff); }

Link: http://lkml.kernel.org/r/20190103145954.16942-2-rpenyaev@suse.de Signed-off-by: Roman Penyaev rpenyaev@suse.de Acked-by: Michal Hocko mhocko@suse.com Cc: Andrey Ryabinin aryabinin@virtuozzo.com Cc: Joe Perches joe@perches.com Cc: "Luis R. Rodriguez" mcgrof@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/vmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/vmalloc.c~mm-vmalloc-fix-size-check-for-remap_vmalloc_range_partial +++ a/mm/vmalloc.c @@ -2249,7 +2249,7 @@ int remap_vmalloc_range_partial(struct v if (!(area->flags & VM_USERMAP)) return -EINVAL;

- if (kaddr + size > area->addr + area->size) + if (kaddr + size > area->addr + get_vm_area_size(area)) return -EINVAL;

do { _