[PATCH v2] IB/isert: wait for deferred control PDU completions before releasing the connection
From: Yehyeong Lee
Date: Fri Aug 21 2026 - 04:06:44 EST
isert_send_done() hands ISTATE_SEND_TASKMGTRSP, ISTATE_SEND_REJECT and
ISTATE_SEND_TEXTRSP completions off to isert_comp_wq and returns. The work
item then runs isert_completion_put() -> isert_put_cmd(), which reads
isert_conn->conn and takes conn->cmd_lock.
Nothing orders that work item against teardown. isert_wait_conn() queues
isert_release_work, which frees isert_conn, and iscsit_close_connection()
frees the iscsit_conn right after it returns, so the queued work can run
against freed memory.
Count the deferred control PDU completions per connection and let
isert_wait_conn() wait for them before the release work is queued.
ISTATE_SEND_LOGOUTRSP is deliberately not counted: that branch runs
iscsit_logout_post_handler(), which ends up waiting for
conn->conn_wait_comp, and that completion is only sent by
iscsit_close_connection() after it has called iscsit_wait_conn().
Waiting for it here would deadlock. Its wait stays the existing
isert_wait4logout().
The splat below is from a kernel with tracing printk()s and an msleep(200)
injected into isert_do_control_comp() to widen the window:
BUG: KASAN: slab-use-after-free in isert_put_cmd+0x53d/0x620
Read of size 8 at addr ffff8881054f1038 by task kworker/u17:1/182
CPU: 0 UID: 0 PID: 182 Comm: kworker/u17:1 Tainted: G B 7.2.0-rc5-TWIDE-gb8babf08acc7 #1 PREEMPT(lazy)
Tainted: [B]=BAD_PAGE
Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: isert_comp_wq isert_do_control_comp
Call Trace:
<TASK>
dump_stack_lvl+0x53/0x70
print_report+0xd0/0x630
? __pfx__raw_spin_lock_irqsave+0x10/0x10
? _raw_spin_unlock_irqrestore+0x3e/0x70
? isert_put_cmd+0x53d/0x620
kasan_report+0xce/0x100
? isert_put_cmd+0x53d/0x620
isert_put_cmd+0x53d/0x620
? isert_completion_put+0x305/0x330
? isert_do_control_comp+0x2ef/0x310
process_one_work+0x633/0x1030
? assign_work+0x11d/0x370
worker_thread+0x45b/0xd10
? __pfx_worker_thread+0x10/0x10
? __pfx_worker_thread+0x10/0x10
kthread+0x2c6/0x3b0
? recalc_sigpending+0x15c/0x1e0
? __pfx_kthread+0x10/0x10
ret_from_fork+0x36e/0x5a0
? __pfx_ret_from_fork+0x10/0x10
? __switch_to+0x572/0xdd0
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
Allocated by task 48:
kasan_save_stack+0x33/0x60
kasan_save_track+0x14/0x30
__kasan_kmalloc+0x8f/0xa0
__kmalloc_cache_noprof+0x158/0x370
isert_cma_handler+0x1e3/0x2ae0
cma_cm_event_handler+0x3e/0x240
cma_ib_req_handler+0x17d9/0x4490
cm_process_work+0x41/0x330
cm_work_handler+0x5727/0xc160
process_one_work+0x633/0x1030
worker_thread+0x45b/0xd10
kthread+0x2c6/0x3b0
ret_from_fork+0x36e/0x5a0
ret_from_fork_asm+0x1a/0x30
Freed by task 184:
kasan_save_stack+0x33/0x60
kasan_save_track+0x14/0x30
kasan_save_free_info+0x3b/0x60
__kasan_slab_free+0x43/0x70
kfree+0x121/0x380
iscsit_close_connection+0x7cf/0x1e60
iscsit_take_action_for_connection_exit+0x1b6/0x360
iscsi_target_tx_thread+0x472/0x690
kthread+0x2c6/0x3b0
ret_from_fork+0x36e/0x5a0
ret_from_fork_asm+0x1a/0x30
Fixes: b8d26b3be8b3 ("iser-target: Add iSCSI Extensions for RDMA (iSER) target driver")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Yehyeong Lee <yhlee@xxxxxxxxxxxxxxxxxx>
---
v2: the counter in v1 was paired with a wait queue embedded in isert_conn.
The waiter reads the count outside that queue's lock, so it could observe
zero and skip the wait entirely. The release work then freed isert_conn
while the last work item was still between its atomic_dec_and_test() and
its wake_up(), which locked the freed queue. Use wait_var_event() and
wake_up_var() instead: those hash the address into a global wait queue
table, so the waker never dereferences isert_conn. The count itself is
unchanged.
The v1 race was pointed out by the Sashiko review bot.
drivers/infiniband/ulp/isert/ib_isert.c | 22 ++++++++++++++++++++++
drivers/infiniband/ulp/isert/ib_isert.h | 2 ++
2 files changed, 24 insertions(+)
diff --git a/drivers/infiniband/ulp/isert/ib_isert.c b/drivers/infiniband/ulp/isert/ib_isert.c
index 1015a51f750af..bc3e69f55054f 100644
--- a/drivers/infiniband/ulp/isert/ib_isert.c
+++ b/drivers/infiniband/ulp/isert/ib_isert.c
@@ -21,6 +21,7 @@
#include <target/target_core_fabric.h>
#include <target/iscsi/iscsi_transport.h>
#include <linux/semaphore.h>
+#include <linux/wait_bit.h>
#include "ib_isert.h"
@@ -308,6 +309,7 @@ isert_init_conn(struct isert_conn *isert_conn)
init_completion(&isert_conn->login_req_comp);
init_waitqueue_head(&isert_conn->rem_wait);
kref_init(&isert_conn->kref);
+ atomic_set(&isert_conn->ctrl_comp_cnt, 0);
mutex_init(&isert_conn->mutex);
INIT_WORK(&isert_conn->release_work, isert_release_work);
}
@@ -1668,6 +1670,8 @@ isert_do_control_comp(struct work_struct *work)
struct isert_conn *isert_conn = isert_cmd->conn;
struct ib_device *ib_dev = isert_conn->cm_id->device;
struct iscsit_cmd *cmd = isert_cmd->iscsit_cmd;
+ /* The switch below may free isert_cmd. */
+ bool counted = isert_cmd->ctrl_counted;
isert_dbg("Cmd %p i_state %d\n", isert_cmd, cmd->i_state);
@@ -1689,6 +1693,14 @@ isert_do_control_comp(struct work_struct *work)
dump_stack();
break;
}
+
+ /*
+ * The count is what keeps isert_conn alive, so drop it last. The wait
+ * queue lives in the global hash table, not in isert_conn, so this is
+ * safe even if the waiter has already freed the connection.
+ */
+ if (counted && atomic_dec_and_test(&isert_conn->ctrl_comp_cnt))
+ wake_up_var(&isert_conn->ctrl_comp_cnt);
}
static void
@@ -1732,6 +1744,12 @@ isert_send_done(struct ib_cq *cq, struct ib_wc *wc)
case ISTATE_SEND_TEXTRSP:
isert_unmap_tx_desc(tx_desc, ib_dev);
+ /* Paired with the wait in isert_wait_conn(). */
+ isert_cmd->ctrl_counted =
+ isert_cmd->iscsit_cmd->i_state != ISTATE_SEND_LOGOUTRSP;
+ if (isert_cmd->ctrl_counted)
+ atomic_inc(&isert_conn->ctrl_comp_cnt);
+
INIT_WORK(&isert_cmd->comp_work, isert_do_control_comp);
queue_work(isert_comp_wq, &isert_cmd->comp_work);
return;
@@ -2572,6 +2590,10 @@ static void isert_wait_conn(struct iscsit_conn *conn)
isert_wait4cmds(conn);
isert_wait4logout(isert_conn);
+ /* Paired with the count taken in isert_send_done(). */
+ wait_var_event(&isert_conn->ctrl_comp_cnt,
+ !atomic_read(&isert_conn->ctrl_comp_cnt));
+
queue_work(isert_release_wq, &isert_conn->release_work);
}
diff --git a/drivers/infiniband/ulp/isert/ib_isert.h b/drivers/infiniband/ulp/isert/ib_isert.h
index 0b2dfd6e7e270..221d2a3376c1f 100644
--- a/drivers/infiniband/ulp/isert/ib_isert.h
+++ b/drivers/infiniband/ulp/isert/ib_isert.h
@@ -153,6 +153,7 @@ struct isert_cmd {
struct work_struct comp_work;
struct scatterlist sg;
bool ctx_init_done;
+ bool ctrl_counted;
};
static inline struct isert_cmd *tx_desc_to_cmd(struct iser_tx_desc *desc)
@@ -186,6 +187,7 @@ struct isert_conn {
struct mutex mutex;
struct kref kref;
struct work_struct release_work;
+ atomic_t ctrl_comp_cnt;
bool logout_posted;
bool snd_w_inv;
wait_queue_head_t rem_wait;
--
2.43.0