Re: [PATCH V2] libceph: fix use after free

[Ilya Dryomov]

On Tue, Nov 27, 2018 at 10:22 AM Pan Bian <bianpan2016@xxxxxxx> wrote:
>
> The function ceph_monc_handle_map calls kfree(old) to free the old
> monitor map, old points to monc->monmap. However, after that, it reads
> monc->monmap->epoch and passes it to __ceph_monc_got_map. This will
> result in a use-after-free bug. The patch moves the free operation after
> the call to __ceph_monc_got_map.
>
> Fixes: 82dcabad750 ("libceph: revamp subs code, switch to SUBSCRIBE2 protocol")
>
> Signed-off-by: Pan Bian <bianpan2016@xxxxxxx>
> ---
> V2: correct the format of the tag Fixes
> ---
>  net/ceph/mon_client.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ceph/mon_client.c b/net/ceph/mon_client.c
> index 18deb3d..05ef5aa 100644
> --- a/net/ceph/mon_client.c
> +++ b/net/ceph/mon_client.c
> @@ -478,9 +478,10 @@ static void ceph_monc_handle_map(struct ceph_mon_client *monc,
>         }
>
>         client->monc.monmap = monmap;

monc->monmap is assigned here.  It's not obvious, but monc->monmap and
client->monc.monmap is the same pointer.

> -       kfree(old);
>
>         __ceph_monc_got_map(monc, CEPH_SUB_MONMAP, monc->monmap->epoch);

ceph_monmap_decode() returns the new map, kfree() frees the old map.
I don't see a use-after-free here.

Thanks,

                Ilya