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    Subject[PATCH 5.10 055/132] nfsd: fix use-after-free due to delegation race
    Date
    From: J. Bruce Fields <bfields@redhat.com>

    commit 548ec0805c399c65ed66c6641be467f717833ab5 upstream.

    A delegation break could arrive as soon as we've called vfs_setlease. A
    delegation break runs a callback which immediately (in
    nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we
    then exit nfs4_set_delegation without hashing the delegation, it will be
    freed as soon as the callback is done with it, without ever being
    removed from del_recall_lru.

    Symptoms show up later as use-after-free or list corruption warnings,
    usually in the laundromat thread.

    I suspect aba2072f4523 "nfsd: grant read delegations to clients holding
    writes" made this bug easier to hit, but I looked as far back as v3.0
    and it looks to me it already had the same problem. So I'm not sure
    where the bug was introduced; it may have been there from the beginning.

    Cc: stable@vger.kernel.org
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/nfsd/nfs4state.c | 9 +++++++--
    1 file changed, 7 insertions(+), 2 deletions(-)

    --- a/fs/nfsd/nfs4state.c
    +++ b/fs/nfsd/nfs4state.c
    @@ -1089,6 +1089,11 @@ hash_delegation_locked(struct nfs4_deleg
    return 0;
    }

    +static bool delegation_hashed(struct nfs4_delegation *dp)
    +{
    + return !(list_empty(&dp->dl_perfile));
    +}
    +
    static bool
    unhash_delegation_locked(struct nfs4_delegation *dp)
    {
    @@ -1096,7 +1101,7 @@ unhash_delegation_locked(struct nfs4_del

    lockdep_assert_held(&state_lock);

    - if (list_empty(&dp->dl_perfile))
    + if (!delegation_hashed(dp))
    return false;

    dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID;
    @@ -4512,7 +4517,7 @@ static void nfsd4_cb_recall_prepare(stru
    * queued for a lease break. Don't queue it again.
    */
    spin_lock(&state_lock);
    - if (dp->dl_time == 0) {
    + if (delegation_hashed(dp) && dp->dl_time == 0) {
    dp->dl_time = ktime_get_boottime_seconds();
    list_add_tail(&dp->dl_recall_lru, &nn->del_recall_lru);
    }

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