Re: [PATCH v2] ceph: avoid putting the realm twice when decoding snaps fails

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On Tue, Nov 8, 2022 at 3:32 AM <xiubli@xxxxxxxxxx> wrote:
>
> From: Xiubo Li <xiubli@xxxxxxxxxx>
>
> When decoding the snaps fails it maybe leaving the 'first_realm'
> and 'realm' pointing to the same snaprealm memory. And then it'll
> put it twice and could cause random use-after-free, BUG_ON, etc
> issues.
>
> Cc: stable@xxxxxxxxxxxxxxx
> URL: https://tracker.ceph.com/issues/57686
> Reviewed-by: Luís Henriques <lhenriques@xxxxxxx>
> Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> ---
>  fs/ceph/snap.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index 9bceed2ebda3..77b948846d4d 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -854,6 +854,8 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc,
>         else
>                 ceph_put_snap_realm(mdsc, realm);
>
> +       realm = NULL;

Hi Xiubo,

Nit: I think it would be better to clear realm in the part of
the function that actually needs it to be cleared -- otherwise
this assignment can be easily lost in refactoring.

        dout("%s deletion=%d\n", __func__, deletion);
more:
        realm = NULL;
        rebuild_snapcs = 0;

And then realm wouldn't need to be initialized.

Thanks,

                Ilya




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