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[PATCH 3.14 27/29] iscsi-target: Fix use-after-free during TPG session shutdown

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3.14-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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/target/iscsi/iscsi_target.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -4709,6 +4709,7 @@ int iscsit_release_sessions_for_tpg(stru
 	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);
@@ -4730,14 +4731,17 @@ int iscsit_release_sessions_for_tpg(stru
 		}
 		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);


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[PATCH 3.14 00/29] 3.14.50-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 11/29] mmc: sdhci-esdhc: Make 8BIT bus work Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
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  [PATCH 3.14 26/29] avr32: handle NULL as a valid clock object Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 07/29] ALSA: usb-audio: add dB range mapping for some devices Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
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  [PATCH 3.14 16/29] blkcg: fix gendisk reference leak in blkg_conf_prep() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 17/29] ata: pmp: add quirk for Marvell 4140 SATA PMP Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 24/29] rds: rds_ib_device.refcount overflow Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 23/29] x86/efi: Use all 64 bit of efi_memmap in setup_e820() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 20/29] xhci: report U3 when link is in resume state Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 10/29] mac80211: clear subdir_stations when removing debugfs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 19/29] xhci: Calculate old endpoints correctly on device reset Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 03/29] s390/sclp: clear upper register halves in _sclp_print_early Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 27/29] iscsi-target: Fix use-after-free during TPG session shutdown Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 02/29] freeing unlinked file indefinitely delayed Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  [PATCH 3.14 01/29] mm: avoid setting up anonymous pages into file mapping Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-09 00:50 +0200
  Re: [PATCH 3.14 00/29] 3.14.50-stable review Guenter Roeck <linux@roeck-us.net> - 2015-08-09 05:20 +0200
    Re: [PATCH 3.14 00/29] 3.14.50-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-08-10 21:20 +0200
  Re: [PATCH 3.14 00/29] 3.14.50-stable review Sudip Mukherjee <sudipm.mukherjee@gmail.com> - 2015-08-10 07:10 +0200

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