Messages in this thread Patch in this message | | | Date | Tue, 26 Mar 2002 22:18:20 +0100 | From | Andrea Arcangeli <> | Subject | Re: [patch] mmap bug with drivers that adjust vm_start |
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On Tue, Mar 26, 2002 at 03:43:45PM -0500, Benjamin LaHaise wrote: > I would rather see an mmap fail if it would collide with an existing mapping, > but that might break some applications.
That doesn't make it easier though, the time we should fail is still way earlier the relocation of the virtual address space area.
> Thanks for looking this over. Cheers,
You're welcome, thanks for fixing it.
> + if (unlikely(NULL != find_vma_prepare(mm, addr, &prev, > + &rb_link, &rb_parent))) {
this looks wrong there may very well be a vma after our mapping but it doesn't necessairly overlap with us (also the unlikely would make more sense in the previous if). I hacked a bit on top of your previous patch, this looks ok to me but it's untested:
diff -urN 2.4.19pre4aa1/mm/mmap.c vma/mm/mmap.c --- 2.4.19pre4aa1/mm/mmap.c Tue Mar 26 20:43:07 2002 +++ vma/mm/mmap.c Tue Mar 26 20:48:24 2002 @@ -554,7 +554,26 @@ * Answer: Yes, several device drivers can do it in their * f_op->mmap method. -DaveM */ - addr = vma->vm_start; + if (unlikely(addr != vma->vm_start)) { + /* + * It is a bit too late to pretend changing the virtual + * area of the mapping, we just corrupted userspace + * in the do_munmap, so FIXME (not in 2.4 to avoid breaking + * the driver API). + */ + struct vm_area_struct * stale_vma; + /* Since addr changed, we rely on the mmap op to prevent + * collisions with existing vmas and just use find_vma_prepare + * to update the tree pointers. + */ + addr = vma->vm_start; + stale_vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent); + /* + * Make sure the lowlevel driver did its job right. + */ + if (unlikely(stale_vma && stale_vma->vm_start < vma->vm_end)) + BUG(); + } vma_link(mm, vma, prev, rb_link, rb_parent); if (correct_wcount)
your printk also is valid debugging trick, I think it won't be necessary most of the time but feel free to re-add it if you like.
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