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    Subject[PATCH 3.13.y-ckt 37/60] iscsi-target: Fix use-after-free during TPG session shutdown
    Date
    3.13.11-ckt26 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Nicholas Bellinger <nab@linux-iscsi.org>

    commit 417c20a9bdd1e876384127cf096d8ae8b559066c upstream.

    This patch fixes a use-after-free bug in iscsit_release_sessions_for_tpg()
    where se_portal_group->session_lock was incorrectly released/re-acquired
    while walking the active se_portal_group->tpg_sess_list.

    The can result in a NULL pointer dereference when iscsit_close_session()
    shutdown happens in the normal path asynchronously to this code, causing
    a bogus dereference of an already freed list entry to occur.

    To address this bug, walk the session list checking for the same state
    as before, but move entries to a local list to avoid dropping the lock
    while walking the active list.

    As before, signal using iscsi_session->session_restatement=1 for those
    list entries to be released locally by iscsit_free_session() code.

    Reported-by: Sunilkumar Nadumuttlu <sjn@datera.io>
    Cc: Sunilkumar Nadumuttlu <sjn@datera.io>
    Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/target/iscsi/iscsi_target.c | 12 ++++++++----
    1 file changed, 8 insertions(+), 4 deletions(-)

    diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
    index 8da53d7..6d70def 100644
    --- a/drivers/target/iscsi/iscsi_target.c
    +++ b/drivers/target/iscsi/iscsi_target.c
    @@ -4708,6 +4708,7 @@ int iscsit_release_sessions_for_tpg(struct iscsi_portal_group *tpg, int force)
    struct iscsi_session *sess;
    struct se_portal_group *se_tpg = &tpg->tpg_se_tpg;
    struct se_session *se_sess, *se_sess_tmp;
    + LIST_HEAD(free_list);
    int session_count = 0;

    spin_lock_bh(&se_tpg->session_lock);
    @@ -4729,14 +4730,17 @@ int iscsit_release_sessions_for_tpg(struct iscsi_portal_group *tpg, int force)
    }
    atomic_set(&sess->session_reinstatement, 1);
    spin_unlock(&sess->conn_lock);
    - spin_unlock_bh(&se_tpg->session_lock);

    - iscsit_free_session(sess);
    - spin_lock_bh(&se_tpg->session_lock);
    + list_move_tail(&se_sess->sess_list, &free_list);
    + }
    + spin_unlock_bh(&se_tpg->session_lock);

    + list_for_each_entry_safe(se_sess, se_sess_tmp, &free_list, sess_list) {
    + sess = (struct iscsi_session *)se_sess->fabric_sess_ptr;
    +
    + iscsit_free_session(sess);
    session_count++;
    }
    - spin_unlock_bh(&se_tpg->session_lock);

    pr_debug("Released %d iSCSI Session(s) from Target Portal"
    " Group: %hu\n", session_count, tpg->tpgt);
    --
    1.9.1


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