On 04/29/2012 01:59 AM, Xi Wang wrote:
> On 32-bit systems, a large `n' would overflow `n * sizeof(u32)' and bypass
> the check ceph_decode_need(p, end, n * sizeof(u32), bad). It would also
> overflow the subsequent kmalloc() size, leading to out-of-bounds write.
This looks good.
Your previous patch made me look at something else though. If
you can think of a good solution would you be willing to send a
patch to implement it? (See below.) I won't hold up committing
this for it, but I'd like your opinion.
Reviewed-by: Alex Elder <elder@xxxxxxxxxxx>
> Signed-off-by: Xi Wang <xi.wang@xxxxxxxxx>
> ---
> net/ceph/osdmap.c | 3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
> index f80afc3..774eac6 100644
> --- a/net/ceph/osdmap.c
> +++ b/net/ceph/osdmap.c
> @@ -670,6 +670,9 @@ struct ceph_osdmap *osdmap_decode(void **p, void *end)
Just above here we see:
/* pg_temp */
ceph_decode_32_safe(p, end, len, bad);
for (i = 0; i < len; i++) {
We haven't validated "len" here either. Looking at it I'm not sure
we can do much, but I think we do know a few things should be true:
- (len & (sizeof (u32) - 1)) == 0
- len <= (UINT_MAX / (sizeof (struct ceph_pg) + sizeof (u32)))
and further, if it's invalid to have a value for pg->len of
zero, then we can instead assert:
- len <= (UINT_MAX / (sizeof (struct ceph_pg) + 2 * sizeof (u32)))
I don't know if it's that important do do a check like this though.
I appreciate these detail-oriented fixes that you've been sending.
> ceph_decode_need(p, end, sizeof(u32) + sizeof(u64), bad);
> ceph_decode_copy(p, &pgid, sizeof(pgid));
> n = ceph_decode_32(p);
> + err = -EINVAL;
> + if (n > (UINT_MAX - sizeof(*pg)) / sizeof(u32))
> + goto bad;
> ceph_decode_need(p, end, n * sizeof(u32), bad);
> err = -ENOMEM;
> pg = kmalloc(sizeof(*pg) + n*sizeof(u32), GFP_NOFS);
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