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authorRoland Dreier <roland@purestorage.com>2012-07-16 22:04:40 +0400
committerNicholas Bellinger <nab@linux-iscsi.org>2012-07-17 04:35:26 +0400
commitbc187ea6c3b3d20bd190f3ee90c954aee0ce8aad (patch)
treea7e9aaf79297e966773504f8df06451808c3df9c /drivers/target
parent7c78b8de267cc4bc63c4f95bda694be606c3644d (diff)
downloadlinux-bc187ea6c3b3d20bd190f3ee90c954aee0ce8aad.tar.xz
target: Check sess_tearing_down in target_get_sess_cmd()
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>
Diffstat (limited to 'drivers/target')
-rw-r--r--drivers/target/target_core_transport.c24
1 files changed, 19 insertions, 5 deletions
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 7b8543480e5f..a979514061e7 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -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)