From: Jann Horn jannh@google.com
commit bdebd6a2831b6fab69eb85cee74a8ba77f1a1cc2 upstream.
remap_vmalloc_range() has had various issues with the bounds checks it promises to perform ("This function checks that addr is a valid vmalloc'ed area, and that it is big enough to cover the vma") over time, e.g.:
- not detecting pgoff<<PAGE_SHIFT overflow
- not detecting (pgoff<<PAGE_SHIFT)+usize overflow
- not checking whether addr and addr+(pgoff<<PAGE_SHIFT) are the same vmalloc allocation
- comparing a potentially wildly out-of-bounds pointer with the end of the vmalloc region
In particular, since commit fc9702273e2e ("bpf: Add mmap() support for BPF_MAP_TYPE_ARRAY"), unprivileged users can cause kernel null pointer dereferences by calling mmap() on a BPF map with a size that is bigger than the distance from the start of the BPF map to the end of the address space.
This could theoretically be used as a kernel ASLR bypass, by using whether mmap() with a given offset oopses or returns an error code to perform a binary search over the possible address range.
To allow remap_vmalloc_range_partial() to verify that addr and addr+(pgoff<<PAGE_SHIFT) are in the same vmalloc region, pass the offset to remap_vmalloc_range_partial() instead of adding it to the pointer in remap_vmalloc_range().
In remap_vmalloc_range_partial(), fix the check against get_vm_area_size() by using size comparisons instead of pointer comparisons, and add checks for pgoff.
Fixes: 833423143c3a ("[PATCH] mm: introduce remap_vmalloc_range()") Signed-off-by: Jann Horn jannh@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Cc: stable@vger.kernel.org Cc: Alexei Starovoitov ast@kernel.org Cc: Daniel Borkmann daniel@iogearbox.net Cc: Martin KaFai Lau kafai@fb.com Cc: Song Liu songliubraving@fb.com Cc: Yonghong Song yhs@fb.com Cc: Andrii Nakryiko andriin@fb.com Cc: John Fastabend john.fastabend@gmail.com Cc: KP Singh kpsingh@chromium.org Link: http://lkml.kernel.org/r/20200415222312.236431-1-jannh@google.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/proc/vmcore.c | 5 +++-- include/linux/vmalloc.h | 2 +- mm/vmalloc.c | 16 +++++++++++++--- samples/vfio-mdev/mdpy.c | 2 +- 4 files changed, 18 insertions(+), 7 deletions(-)
--- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -266,7 +266,8 @@ static int vmcoredd_mmap_dumps(struct vm if (start < offset + dump->size) { tsz = min(offset + (u64)dump->size - start, (u64)size); buf = dump->buf + start - offset; - if (remap_vmalloc_range_partial(vma, dst, buf, tsz)) { + if (remap_vmalloc_range_partial(vma, dst, buf, 0, + tsz)) { ret = -EFAULT; goto out_unlock; } @@ -624,7 +625,7 @@ static int mmap_vmcore(struct file *file tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)start, size); kaddr = elfnotes_buf + start - elfcorebuf_sz - vmcoredd_orig_sz; if (remap_vmalloc_range_partial(vma, vma->vm_start + len, - kaddr, tsz)) + kaddr, 0, tsz)) goto fail;
size -= tsz; --- a/include/linux/vmalloc.h +++ b/include/linux/vmalloc.h @@ -122,7 +122,7 @@ extern void vunmap(const void *addr);
extern int remap_vmalloc_range_partial(struct vm_area_struct *vma, unsigned long uaddr, void *kaddr, - unsigned long size); + unsigned long pgoff, unsigned long size);
extern int remap_vmalloc_range(struct vm_area_struct *vma, void *addr, unsigned long pgoff); --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -34,6 +34,7 @@ #include <linux/llist.h> #include <linux/bitops.h> #include <linux/rbtree_augmented.h> +#include <linux/overflow.h>
#include <linux/uaccess.h> #include <asm/tlbflush.h> @@ -2976,6 +2977,7 @@ finished: * @vma: vma to cover * @uaddr: target user address to start at * @kaddr: virtual address of vmalloc kernel memory + * @pgoff: offset from @kaddr to start at * @size: size of map area * * Returns: 0 for success, -Exxx on failure @@ -2988,9 +2990,15 @@ finished: * Similar to remap_pfn_range() (see mm/memory.c) */ int remap_vmalloc_range_partial(struct vm_area_struct *vma, unsigned long uaddr, - void *kaddr, unsigned long size) + void *kaddr, unsigned long pgoff, + unsigned long size) { struct vm_struct *area; + unsigned long off; + unsigned long end_index; + + if (check_shl_overflow(pgoff, PAGE_SHIFT, &off)) + return -EINVAL;
size = PAGE_ALIGN(size);
@@ -3004,8 +3012,10 @@ int remap_vmalloc_range_partial(struct v if (!(area->flags & (VM_USERMAP | VM_DMA_COHERENT))) return -EINVAL;
- if (kaddr + size > area->addr + get_vm_area_size(area)) + if (check_add_overflow(size, off, &end_index) || + end_index > get_vm_area_size(area)) return -EINVAL; + kaddr += off;
do { struct page *page = vmalloc_to_page(kaddr); @@ -3044,7 +3054,7 @@ int remap_vmalloc_range(struct vm_area_s unsigned long pgoff) { return remap_vmalloc_range_partial(vma, vma->vm_start, - addr + (pgoff << PAGE_SHIFT), + addr, pgoff, vma->vm_end - vma->vm_start); } EXPORT_SYMBOL(remap_vmalloc_range); --- a/samples/vfio-mdev/mdpy.c +++ b/samples/vfio-mdev/mdpy.c @@ -418,7 +418,7 @@ static int mdpy_mmap(struct mdev_device return -EINVAL;
return remap_vmalloc_range_partial(vma, vma->vm_start, - mdev_state->memblk, + mdev_state->memblk, 0, vma->vm_end - vma->vm_start); }