From c1ddc7b785b4ad724994834ffc671d620be1d060 Mon Sep 17 00:00:00 2001 From: Roman Penyaev Date: Tue, 5 Mar 2019 15:43:20 -0800 Subject: mm/vmalloc: fix size check for remap_vmalloc_range_partial() commit 401592d2e095947344e10ec0623adbcd58934dd4 upstream. 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 Acked-by: Michal Hocko Cc: Andrey Ryabinin Cc: Joe Perches Cc: "Luis R. Rodriguez" Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/vmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm') diff --git a/mm/vmalloc.c b/mm/vmalloc.c index a728fc492557..91a789a46b12 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2244,7 +2244,7 @@ int remap_vmalloc_range_partial(struct vm_area_struct *vma, unsigned long uaddr, 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 { -- cgit v1.2.3