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target: Check sess_tearing_down in target_get_sess_cmd()

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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.

(nab: Keep target_submit_cmd() returning void for now..)

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
This commit is contained in:
Roland Dreier 2012-07-16 11:04:40 -07:00 committed by Nicholas Bellinger
parent 7c78b8de26
commit bc187ea6c3
1 changed files with 19 additions and 5 deletions
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24
drivers/target/target_core_transport.c
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@ -70,7 +70,7 @@ 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 int transport_set_sense_codes(struct se_cmd *cmd, u8 asc, u8 ascq);
static void target_complete_ok_work(struct work_struct *work);
@ -1477,7 +1477,9 @@ void 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;
/*
* Signal bidirectional data payloads to target-core
*/
@ -1561,7 +1563,11 @@ 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) {
@ -2409,10 +2415,11 @@ 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);
/*
@ -2426,9 +2433,16 @@ 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)