From patchwork Tue Oct 11 14:17:06 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [1/3] mm: avoid wrapping vm_pgoff in mremap() - CVE-2011-2496 Date: Tue, 11 Oct 2011 04:17:06 -0000 From: Paolo Pisati X-Patchwork-Id: 118991 Message-Id: <1318342628-32016-2-git-send-email-paolo.pisati@canonical.com> To: kernel-team@lists.ubuntu.com From: 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. BugLink: http://bugs.launchpad.net/bugs/869243 commit upstream 982134ba62618c2d69fbbbd166d0a11ee3b7e3d8 Reported-and-tested-by: Robert Swiecki Acked-by: Hugh Dickins Cc: stable@kernel.org Signed-off-by: Linus Torvalds Signed-off-by: Paolo Pisati --- mm/mremap.c | 11 +++++++++-- 1 files changed, 9 insertions(+), 2 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index f61efb2..eefaeab 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -255,9 +255,16 @@ 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) {