From: Benjamin Block <bblock@xxxxxxxxxxxxx>
commit b76becde2b84137faa29bbc9a3b20953b5980e48 upstream.
With a recent change to our send path for FSF commands we introduced a
possible use-after-free of request-objects, that might further lead to
zfcp crafting bad requests, which the FCP channel correctly complains
about with an error (FSF_PROT_SEQ_NUMB_ERROR). This error is then handled
by an adapter-wide recovery.
The following sequence illustrates the possible use-after-free:
Send Path:
int zfcp_fsf_open_port(struct zfcp_erp_action *erp_action)
{
struct zfcp_fsf_req *req;
...
spin_lock_irq(&qdio->req_q_lock);
// ^^^^^^^^^^^^^^^^
// protects QDIO queue during sending
...
req = zfcp_fsf_req_create(qdio,
FSF_QTCB_OPEN_PORT_WITH_DID,
SBAL_SFLAGS0_TYPE_READ,
qdio->adapter->pool.erp_req);
// ^^^^^^^^^^^^^^^^^^^
// allocation of the request-object
...
retval = zfcp_fsf_req_send(req);
...
spin_unlock_irq(&qdio->req_q_lock);
return retval;
}
static int zfcp_fsf_req_send(struct zfcp_fsf_req *req)
{
struct zfcp_adapter *adapter = req->adapter;
struct zfcp_qdio *qdio = adapter->qdio;
...
zfcp_reqlist_add(adapter->req_list, req);
// ^^^^^^^^^^^^^^^^
// add request to our driver-internal hash-table for tracking
// (protected by separate lock req_list->lock)
...
if (zfcp_qdio_send(qdio, &req->qdio_req)) {
// ^^^^^^^^^^^^^^
// hand-off the request to FCP channel;
// the request can complete at any point now
...
}
/* Don't increase for unsolicited status */
if (!zfcp_fsf_req_is_status_read_buffer(req))
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
// possible use-after-free
adapter->fsf_req_seq_no++;
// ^^^^^^^^^^^^^^^^
// because of the use-after-free we might
// miss this accounting, and as follow-up
// this results in the FCP channel error
// FSF_PROT_SEQ_NUMB_ERROR
adapter->req_no++;
return 0;
}
static inline bool
zfcp_fsf_req_is_status_read_buffer(struct zfcp_fsf_req *req)
{
return req->qtcb == NULL;
// ^^^^^^^^^
// possible use-after-free
}
Response Path:
void zfcp_fsf_reqid_check(struct zfcp_qdio *qdio, int sbal_idx)
{
...
struct zfcp_fsf_req *fsf_req;
...
for (idx = 0; idx < QDIO_MAX_ELEMENTS_PER_BUFFER; idx++) {
...
fsf_req = zfcp_reqlist_find_rm(adapter->req_list,
req_id);
// ^^^^^^^^^^^^^^^^^^^^
// remove request from our driver-internal
// hash-table (lock req_list->lock)
...
zfcp_fsf_req_complete(fsf_req);
}
}
static void zfcp_fsf_req_complete(struct zfcp_fsf_req *req)
{
...
if (likely(req->status & ZFCP_STATUS_FSFREQ_CLEANUP))
zfcp_fsf_req_free(req);
// ^^^^^^^^^^^^^^^^^
// free memory for request-object
else
complete(&req->completion);
// ^^^^^^^^
// completion notification for code-paths that wait
// synchronous for the completion of the request; in
// those the memory is freed separately
}
The result of the use-after-free only affects the send path, and can not
lead to any data corruption. In case we miss the sequence-number
accounting, because the memory was already re-purposed, the next FSF
command will fail with said FCP channel error, and we will recover the
whole adapter. This causes no additional errors, but it slows down
traffic. There is a slight chance of the same thing happen again
recursively after the adapter recovery, but so far this has not been seen.
This was seen under z/VM, where the send path might run on a virtual CPU
that gets scheduled away by z/VM, while the return path might still run,
and so create the necessary timing. Running with KASAN can also slow down
the kernel sufficiently to run into this user-after-free, and then see the
report by KASAN.
To fix this, simply pull the test for the sequence-number accounting in
front of the hand-off to the FCP channel (this information doesn't change
during hand-off), but leave the sequence-number accounting itself where it
is.
To make future regressions of the same kind less likely, add comments to
all closely related code-paths.
Signed-off-by: Benjamin Block <bblock@xxxxxxxxxxxxx>
Fixes: f9eca0227600 ("scsi: zfcp: drop duplicate fsf_command from zfcp_fsf_req which is also in QTCB header")
Cc: <stable@xxxxxxxxxxxxxxx> #5.0+
Reviewed-by: Steffen Maier <maier@xxxxxxxxxxxxx>
Reviewed-by: Jens Remus <jremus@xxxxxxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/s390/scsi/zfcp_fsf.c | 45 ++++++++++++++++++++++++++++++++++++++-----
1 file changed, 40 insertions(+), 5 deletions(-)
--- a/drivers/s390/scsi/zfcp_fsf.c
+++ b/drivers/s390/scsi/zfcp_fsf.c
@@ -11,6 +11,7 @@
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
#include <linux/blktrace_api.h>
+#include <linux/types.h>
#include <linux/slab.h>
#include <scsi/fc/fc_els.h>
#include "zfcp_ext.h"
@@ -741,6 +742,7 @@ static struct zfcp_fsf_req *zfcp_fsf_req
static int zfcp_fsf_req_send(struct zfcp_fsf_req *req)
{
+ const bool is_srb = zfcp_fsf_req_is_status_read_buffer(req);
struct zfcp_adapter *adapter = req->adapter;
struct zfcp_qdio *qdio = adapter->qdio;
int req_id = req->req_id;
@@ -757,8 +759,20 @@ static int zfcp_fsf_req_send(struct zfcp
return -EIO;
}
+ /*
+ * NOTE: DO NOT TOUCH ASYNC req PAST THIS POINT.
+ * ONLY TOUCH SYNC req AGAIN ON req->completion.
+ *
+ * The request might complete and be freed concurrently at any point
+ * now. This is not protected by the QDIO-lock (req_q_lock). So any
+ * uncontrolled access after this might result in an use-after-free bug.
+ * Only if the request doesn't have ZFCP_STATUS_FSFREQ_CLEANUP set, and
+ * when it is completed via req->completion, is it safe to use req
+ * again.
+ */
+
/* Don't increase for unsolicited status */
- if (!zfcp_fsf_req_is_status_read_buffer(req))
+ if (!is_srb)
adapter->fsf_req_seq_no++;
adapter->req_no++;
@@ -805,6 +819,7 @@ int zfcp_fsf_status_read(struct zfcp_qdi
retval = zfcp_fsf_req_send(req);
if (retval)
goto failed_req_send;
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
goto out;
@@ -914,8 +929,10 @@ struct zfcp_fsf_req *zfcp_fsf_abort_fcp_
req->qtcb->bottom.support.req_handle = (u64) old_req_id;
zfcp_fsf_start_timer(req, ZFCP_FSF_SCSI_ER_TIMEOUT);
- if (!zfcp_fsf_req_send(req))
+ if (!zfcp_fsf_req_send(req)) {
+ /* NOTE: DO NOT TOUCH req, UNTIL IT COMPLETES! */
goto out;
+ }
out_error_free:
zfcp_fsf_req_free(req);
@@ -1098,6 +1115,7 @@ int zfcp_fsf_send_ct(struct zfcp_fc_wka_
ret = zfcp_fsf_req_send(req);
if (ret)
goto failed_send;
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
goto out;
@@ -1198,6 +1216,7 @@ int zfcp_fsf_send_els(struct zfcp_adapte
ret = zfcp_fsf_req_send(req);
if (ret)
goto failed_send;
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
goto out;
@@ -1243,6 +1262,7 @@ int zfcp_fsf_exchange_config_data(struct
zfcp_fsf_req_free(req);
erp_action->fsf_req_id = 0;
}
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
out:
spin_unlock_irq(&qdio->req_q_lock);
return retval;
@@ -1279,8 +1299,10 @@ int zfcp_fsf_exchange_config_data_sync(s
zfcp_fsf_start_timer(req, ZFCP_FSF_REQUEST_TIMEOUT);
retval = zfcp_fsf_req_send(req);
spin_unlock_irq(&qdio->req_q_lock);
- if (!retval)
+ if (!retval) {
+ /* NOTE: ONLY TOUCH SYNC req AGAIN ON req->completion. */
wait_for_completion(&req->completion);
+ }
zfcp_fsf_req_free(req);
return retval;
@@ -1330,6 +1352,7 @@ int zfcp_fsf_exchange_port_data(struct z
zfcp_fsf_req_free(req);
erp_action->fsf_req_id = 0;
}
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
out:
spin_unlock_irq(&qdio->req_q_lock);
return retval;
@@ -1372,8 +1395,10 @@ int zfcp_fsf_exchange_port_data_sync(str
retval = zfcp_fsf_req_send(req);
spin_unlock_irq(&qdio->req_q_lock);
- if (!retval)
+ if (!retval) {
+ /* NOTE: ONLY TOUCH SYNC req AGAIN ON req->completion. */
wait_for_completion(&req->completion);
+ }
zfcp_fsf_req_free(req);
@@ -1493,6 +1518,7 @@ int zfcp_fsf_open_port(struct zfcp_erp_a
erp_action->fsf_req_id = 0;
put_device(&port->dev);
}
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
out:
spin_unlock_irq(&qdio->req_q_lock);
return retval;
@@ -1557,6 +1583,7 @@ int zfcp_fsf_close_port(struct zfcp_erp_
zfcp_fsf_req_free(req);
erp_action->fsf_req_id = 0;
}
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
out:
spin_unlock_irq(&qdio->req_q_lock);
return retval;
@@ -1626,6 +1653,7 @@ int zfcp_fsf_open_wka_port(struct zfcp_f
retval = zfcp_fsf_req_send(req);
if (retval)
zfcp_fsf_req_free(req);
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
out:
spin_unlock_irq(&qdio->req_q_lock);
if (!retval)
@@ -1681,6 +1709,7 @@ int zfcp_fsf_close_wka_port(struct zfcp_
retval = zfcp_fsf_req_send(req);
if (retval)
zfcp_fsf_req_free(req);
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
out:
spin_unlock_irq(&qdio->req_q_lock);
if (!retval)
@@ -1776,6 +1805,7 @@ int zfcp_fsf_close_physical_port(struct
zfcp_fsf_req_free(req);
erp_action->fsf_req_id = 0;
}
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
out:
spin_unlock_irq(&qdio->req_q_lock);
return retval;
@@ -1899,6 +1929,7 @@ int zfcp_fsf_open_lun(struct zfcp_erp_ac
zfcp_fsf_req_free(req);
erp_action->fsf_req_id = 0;
}
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
out:
spin_unlock_irq(&qdio->req_q_lock);
return retval;
@@ -1987,6 +2018,7 @@ int zfcp_fsf_close_lun(struct zfcp_erp_a
zfcp_fsf_req_free(req);
erp_action->fsf_req_id = 0;
}
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
out:
spin_unlock_irq(&qdio->req_q_lock);
return retval;
@@ -2299,6 +2331,7 @@ int zfcp_fsf_fcp_cmnd(struct scsi_cmnd *
retval = zfcp_fsf_req_send(req);
if (unlikely(retval))
goto failed_scsi_cmnd;
+ /* NOTE: DO NOT TOUCH req PAST THIS POINT! */
goto out;
@@ -2373,8 +2406,10 @@ struct zfcp_fsf_req *zfcp_fsf_fcp_task_m
zfcp_fc_fcp_tm(fcp_cmnd, sdev, tm_flags);
zfcp_fsf_start_timer(req, ZFCP_FSF_SCSI_ER_TIMEOUT);
- if (!zfcp_fsf_req_send(req))
+ if (!zfcp_fsf_req_send(req)) {
+ /* NOTE: DO NOT TOUCH req, UNTIL IT COMPLETES! */
goto out;
+ }
zfcp_fsf_req_free(req);
req = NULL;
