Commit 982134ba authored Apr 07, 2011 by Linus Torvalds

mm: avoid wrapping vm_pgoff in mremap()



The normal mmap paths all avoid creating a mapping where the pgoff
inside the mapping could wrap around due to overflow.  However, an
expanding mremap() can take such a non-wrapping mapping and make it
bigger and cause a wrapping condition.

Noticed by Robert Swiecki when running a system call fuzzer, where it
caused a BUG_ON() due to terminally confusing the vma_prio_tree code.  A
vma dumping patch by Hugh then pinpointed the crazy wrapped case.

Reported-and-tested-by: Robert Swiecki <robert@swiecki.net>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 6221f222

mm/mremap.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -277,9 +277,16 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
		if (old_len > vma->vm_end - addr)
		goto Efault;

		if (vma->vm_flags & (VM_DONTEXPAND \| VM_PFNMAP)) {
		if (new_len > old_len)
		/* Need to be careful about a growing mapping */
		if (new_len > old_len) {
		unsigned long pgoff;

		if (vma->vm_flags & (VM_DONTEXPAND \| VM_PFNMAP))
		goto Efault;
		pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
		pgoff += vma->vm_pgoff;
		if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
		goto Einval;
		}

		if (vma->vm_flags & VM_LOCKED) {