Re: rbd: refactor rbd_header_from_disk()

[Alex Elder <alex.elder@linaro.org>]

On 06/20/2013 04:11 PM, Dan Carpenter wrote:
> Hello Alex Elder,
> 
> The patch bb23e37acb2a: "rbd: refactor rbd_header_from_disk()" from 
> May 6, 2013, has some integer overflow bugs:
> 
> drivers/block/rbd.c
>    793          snap_count = le32_to_cpu(ondisk->snap_count);
>    794          snapc = ceph_create_snap_context(snap_count, GFP_KERNEL);
> 
> snap_count comes from the disk.  On 32 bit systems there is an integer
> overflow problem inside ceph_create_snap_context() so snapc could be
> smaller than intended.

Is it true that fixing ceph_create_snap_context() would resolve
the issues you describe here?

I believe inserting this at the top of that function would
resolve the potential overflow:

        if (snap_count > SNAP_COUNT_MAX)
                return NULL;

Where SNAP_COUNT_MAX would be defined as:

#define SNAP_COUNT_MAX \
        ((SIZE_MAX - sizeof (struct ceph_snap_context)) / sizeof (u64))

Do you agree, or is there something else you would recommend?
Thanks.

					-Alex
> 
>    795          if (!snapc)
>    796                  goto out_err;
>    797          snapc->seq = le64_to_cpu(ondisk->snap_seq);
>    798          if (snap_count) {
>    799                  struct rbd_image_snap_ondisk *snaps;
>    800                  u64 snap_names_len = le64_to_cpu(ondisk->snap_names_len);
>    801  
>    802                  /* We'll keep a copy of the snapshot names... */
>    803  
>    804                  if (snap_names_len > (u64)SIZE_MAX)
>    805                          goto out_2big;
>    806                  snap_names = kmalloc(snap_names_len, GFP_KERNEL);
>    807                  if (!snap_names)
>    808                          goto out_err;
>    809  
>    810                  /* ...as well as the array of their sizes. */
>    811  
>    812                  size = snap_count * sizeof (*header->snap_sizes);
>                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> There is a second integer overflow bug here.
> 
>    813                  snap_sizes = kmalloc(size, GFP_KERNEL);
>    814                  if (!snap_sizes)
>    815                          goto out_err;
> 
> regards,
> dan carpenter
>