From: Roland Dreier <roland@xxxxxxxxxxxxxxx>
Target core code assumes that target_splice_sess_cmd_list() has set
sess_tearing_down and moved the list of pending commands to
sess_wait_list, no more commands will be added to the session; if any
are added, nothing keeps the se_session from being freed while the
command is still in flight, which e.g. leads to use-after-free of
se_cmd->se_sess in target_release_cmd_kref().
To enforce this invariant, put a check of sess_tearing_down inside of
sess_cmd_lock in target_get_sess_cmd(); any checks before this are
racy and can lead to the use-after-free described above. For example,
the qla_target check in qlt_do_work() checks sess_tearing_down from
work thread context but then drops all locks before calling
target_submit_cmd() (as it must, since that is a sleeping function).
However, since no locks are held, anything can happen with respect to
the session it has looked up -- although it does correctly get
sess_kref within its lock, so the memory won't be freed while
target_submit_cmd() is actually running, nothing stops eg an ACL from
being dropped and calling ->shutdown_session() (which calls into
target_splice_sess_cmd_list()) before we get to target_get_sess_cmd().
Once this happens, the se_session memory can be freed as soon as
target_submit_cmd() returns and qlt_do_work() drops its reference,
even though we've just added a command to sess_cmd_list.
To prevent this use-after-free, check sess_tearing_down inside of
sess_cmd_lock right before target_get_sess_cmd() adds a command to
sess_cmd_list; this is synchronized with target_splice_sess_cmd_list()
so that every command is either waited for or not added to the queue.
Signed-off-by: Roland Dreier <roland@xxxxxxxxxxxxxxx>
---
drivers/target/target_core_transport.c | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 34ca821..23e6e2d 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -73,7 +73,7 @@ static void transport_complete_task_attr(struct se_cmd *cmd);
static void transport_handle_queue_full(struct se_cmd *cmd,
struct se_device *dev);
static int transport_generic_get_mem(struct se_cmd *cmd);
-static void target_get_sess_cmd(struct se_session *, struct se_cmd *, bool);
+static int target_get_sess_cmd(struct se_session *, struct se_cmd *, bool);
static void transport_put_cmd(struct se_cmd *cmd);
static void transport_remove_cmd_from_queue(struct se_cmd *cmd);
static int transport_set_sense_codes(struct se_cmd *cmd, u8 asc, u8 ascq);
@@ -1570,7 +1570,9 @@ int target_submit_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
* for fabrics using TARGET_SCF_ACK_KREF that expect a second
* kref_put() to happen during fabric packet acknowledgement.
*/
- target_get_sess_cmd(se_sess, se_cmd, (flags & TARGET_SCF_ACK_KREF));
+ rc = target_get_sess_cmd(se_sess, se_cmd, (flags & TARGET_SCF_ACK_KREF));
+ if (rc)
+ return rc;
/*
* Signal bidirectional data payloads to target-core
*/
@@ -1664,7 +1666,11 @@ int target_submit_tmr(struct se_cmd *se_cmd, struct se_session *se_sess,
se_cmd->se_tmr_req->ref_task_tag = tag;
/* See target_submit_cmd for commentary */
- target_get_sess_cmd(se_sess, se_cmd, (flags & TARGET_SCF_ACK_KREF));
+ ret = target_get_sess_cmd(se_sess, se_cmd, (flags & TARGET_SCF_ACK_KREF));
+ if (ret) {
+ core_tmr_release_req(se_cmd->se_tmr_req);
+ return ret;
+ }
ret = transport_lookup_tmr_lun(se_cmd, unpacked_lun);
if (ret) {
@@ -3650,10 +3656,11 @@ EXPORT_SYMBOL(transport_generic_free_cmd);
* @se_cmd: command descriptor to add
* @ack_kref: Signal that fabric will perform an ack target_put_sess_cmd()
*/
-static void target_get_sess_cmd(struct se_session *se_sess, struct se_cmd *se_cmd,
- bool ack_kref)
+static int target_get_sess_cmd(struct se_session *se_sess, struct se_cmd *se_cmd,
+ bool ack_kref)
{
unsigned long flags;
+ int ret = 0;
kref_init(&se_cmd->cmd_kref);
/*
@@ -3667,9 +3674,16 @@ static void target_get_sess_cmd(struct se_session *se_sess, struct se_cmd *se_cm
}
spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
+ if (se_sess->sess_tearing_down) {
+ ret = -ESHUTDOWN;
+ goto out;
+ }
list_add_tail(&se_cmd->se_cmd_list, &se_sess->sess_cmd_list);
se_cmd->check_release = 1;
+
+out:
spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
+ return ret;
}
static void target_release_cmd_kref(struct kref *kref)
--
1.7.10.4
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