[PATCH 3.4 048/107] iscsi-target: Fix use-after-free during TPG session shutdown

From: lizf
Date: Wed Mar 16 2016 - 04:10:05 EST

From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>

3.4.111-rc1 review patch. If anyone has any objections, please let me know.


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@xxxxxxxxx>
Cc: Sunilkumar Nadumuttlu <sjn@xxxxxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx>
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 56d02e0..79665f3 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -4500,6 +4500,7 @@ 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;

@@ -4521,14 +4522,17 @@ int iscsit_release_sessions_for_tpg(struct iscsi_portal_group *tpg, int force)
atomic_set(&sess->session_reinstatement, 1);
- 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);
- spin_unlock_bh(&se_tpg->session_lock);

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