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

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On Mon, Nov 7, 2022 at 8:18 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
> Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> ---
>  fs/ceph/snap.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index 9bceed2ebda3..baf17df05107 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -849,10 +849,12 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc,
>         if (realm_to_rebuild && p >= e)
>                 rebuild_snap_realms(realm_to_rebuild, &dirty_realms);
>
> -       if (!first_realm)
> +       if (!first_realm) {
>                 first_realm = realm;
> -       else
> +               realm = NULL;

Hi Xiubo,

I wonder why realm is cleared only in !first_realm branch?  Can't
the same issue occur with realm?

    first_realm is already set, ceph_put_snap_realm(realm)
    p < e, goto more
    decoding fails, goto bad
    realm is still set and not IS_ERR, ceph_put_snap_realm(realm)
    <realm is put twice>

Thanks,

                Ilya



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