IB/srp: Fix a race condition

Avoid a crash caused by the scmnd->scsi_done(scmnd) call in
srp_process_rsp() being invoked with scsi_done == NULL.  This can
happen if a reply is received during or after a command abort.

Reported-by: Joseph Glanville <joseph.glanville@orionvm.com.au>
Reference: http://marc.info/?l=linux-rdma&m=134314367801595
Cc: <stable@vger.kernel.org>
Acked-by: David Dillow <dillowda@ornl.gov>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 63 insertions, 24 deletions

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index bcbf22ee0aa7..1b5b0c730054 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -586,24 +586,62 @@ static void srp_unmap_data(struct scsi_cmnd *scmnd,
                         scmnd->sc_data_direction);
 }
 
-static void srp_remove_req(struct srp_target_port *target,
-                           struct srp_request *req, s32 req_lim_delta)
+/**
+ * srp_claim_req - Take ownership of the scmnd associated with a request.
+ * @target: SRP target port.
+ * @req: SRP request.
+ * @scmnd: If NULL, take ownership of @req->scmnd. If not NULL, only take
+ *         ownership of @req->scmnd if it equals @scmnd.
+ *
+ * Return value:
+ * Either NULL or a pointer to the SCSI command the caller became owner of.
+ */
+static struct scsi_cmnd *srp_claim_req(struct srp_target_port *target,
+                                       struct srp_request *req,
+                                       struct scsi_cmnd *scmnd)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&target->lock, flags);
+        if (!scmnd) {
+                scmnd = req->scmnd;
+                req->scmnd = NULL;
+        } else if (req->scmnd == scmnd) {
+                req->scmnd = NULL;
+        } else {
+                scmnd = NULL;
+        }
+        spin_unlock_irqrestore(&target->lock, flags);
+
+        return scmnd;
+}
+
+/**
+ * srp_free_req() - Unmap data and add request to the free request list.
+ */
+static void srp_free_req(struct srp_target_port *target,
+                         struct srp_request *req, struct scsi_cmnd *scmnd,
+                         s32 req_lim_delta)
 {
         unsigned long flags;
 
-        srp_unmap_data(req->scmnd, target, req);
+        srp_unmap_data(scmnd, target, req);
+
         spin_lock_irqsave(&target->lock, flags);
         target->req_lim += req_lim_delta;
-        req->scmnd = NULL;
         list_add_tail(&req->list, &target->free_reqs);
         spin_unlock_irqrestore(&target->lock, flags);
 }
 
 static void srp_reset_req(struct srp_target_port *target, struct srp_request *req)
 {
-        req->scmnd->result = DID_RESET << 16;
-        req->scmnd->scsi_done(req->scmnd);
-        srp_remove_req(target, req, 0);
+        struct scsi_cmnd *scmnd = srp_claim_req(target, req, NULL);
+
+        if (scmnd) {
+                scmnd->result = DID_RESET << 16;
+                scmnd->scsi_done(scmnd);
+                srp_free_req(target, req, scmnd, 0);
+        }
 }
 
 static int srp_reconnect_target(struct srp_target_port *target)
@@ -1073,11 +1111,18 @@ static void srp_process_rsp(struct srp_target_port *target, struct srp_rsp *rsp)
                 complete(&target->tsk_mgmt_done);
         } else {
                 req = &target->req_ring[rsp->tag];
-                scmnd = req->scmnd;
-                if (!scmnd)
+                scmnd = srp_claim_req(target, req, NULL);
+                if (!scmnd) {
                         shost_printk(KERN_ERR, target->scsi_host,
                                      "Null scmnd for RSP w/tag %016llx\n",
                                      (unsigned long long) rsp->tag);
+
+                        spin_lock_irqsave(&target->lock, flags);
+                        target->req_lim += be32_to_cpu(rsp->req_lim_delta);
+                        spin_unlock_irqrestore(&target->lock, flags);
+
+                        return;
+                }
                 scmnd->result = rsp->status;
 
                 if (rsp->flags & SRP_RSP_FLAG_SNSVALID) {
@@ -1092,7 +1137,9 @@ static void srp_process_rsp(struct srp_target_port *target, struct srp_rsp *rsp)
                 else if (rsp->flags & (SRP_RSP_FLAG_DIOVER | SRP_RSP_FLAG_DIUNDER))
                         scsi_set_resid(scmnd, be32_to_cpu(rsp->data_in_res_cnt));
 
-                srp_remove_req(target, req, be32_to_cpu(rsp->req_lim_delta));
+                srp_free_req(target, req, scmnd,
+                             be32_to_cpu(rsp->req_lim_delta));
+
                 scmnd->host_scribble = NULL;
                 scmnd->scsi_done(scmnd);
         }
@@ -1631,25 +1678,17 @@ static int srp_abort(struct scsi_cmnd *scmnd)
 {
         struct srp_target_port *target = host_to_target(scmnd->device->host);
         struct srp_request *req = (struct srp_request *) scmnd->host_scribble;
-        int ret = SUCCESS;
 
         shost_printk(KERN_ERR, target->scsi_host, "SRP abort called\n");
 
-        if (!req || target->qp_in_error)
+        if (!req || target->qp_in_error || !srp_claim_req(target, req, scmnd))
                 return FAILED;
-        if (srp_send_tsk_mgmt(target, req->index, scmnd->device->lun,
-                              SRP_TSK_ABORT_TASK))
-                return FAILED;
-
-        if (req->scmnd) {
-                if (!target->tsk_mgmt_status) {
-                        srp_remove_req(target, req, 0);
-                        scmnd->result = DID_ABORT << 16;
-                } else
-                        ret = FAILED;
-        }
+        srp_send_tsk_mgmt(target, req->index, scmnd->device->lun,
+                          SRP_TSK_ABORT_TASK);
+        srp_free_req(target, req, scmnd, 0);
+        scmnd->result = DID_ABORT << 16;
 
-        return ret;
+        return SUCCESS;
 }
 
 static int srp_reset_device(struct scsi_cmnd *scmnd)