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mm: avoid wrapping vm_pgoff in mremap()

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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>
This commit is contained in:
Linus Torvalds 2011-04-07 07:35:50 -07:00
commit 982134ba62
1 changed files with 9 additions and 2 deletions
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11
mm/mremap.c
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@ -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) {