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vmalloc: fix remap_vmalloc_range() bounds checks

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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: 833423143c ("[PATCH] mm: introduce remap_vmalloc_range()")
Signed-off-by: Jann Horn <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: [email protected]
Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: KP Singh <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Jann Horn 2020-04-20 18:14:11 -07:00 • committed by Greg Kroah-Hartman
commit f4f235309b
4 changed files with 18 additions and 7 deletions
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5
fs/proc/vmcore.c
View file

@ -266,7 +266,8 @@ static int vmcoredd_mmap_dumps(struct vm_area_struct *vma, unsigned long dst,
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, struct vm_area_struct *vma)
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;