hw/nvme: remove copy bh scheduling

Fix a potential use-after-free by removing the bottom half and enqueuing
the completion directly.

Fixes: 796d20681d ("hw/nvme: reimplement the copy command to allow aio cancellation")
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>

hw/nvme/ctrl.c

@@ -2552,7 +2552,6 @@ typedef struct NvmeCopyAIOCB {
     BlockAIOCB common;
     BlockAIOCB *aiocb;
     NvmeRequest *req;
-    QEMUBH *bh;
     int ret;
 
     void *ranges;
@@ -2590,9 +2589,8 @@ static const AIOCBInfo nvme_copy_aiocb_info = {
     .cancel_async = nvme_copy_cancel,
 };
 
-static void nvme_copy_bh(void *opaque)
+static void nvme_copy_done(NvmeCopyAIOCB *iocb)
 {
-    NvmeCopyAIOCB *iocb = opaque;
     NvmeRequest *req = iocb->req;
     NvmeNamespace *ns = req->ns;
     BlockAcctStats *stats = blk_get_stats(ns->blkconf.blk);
@@ -2604,9 +2602,6 @@ static void nvme_copy_bh(void *opaque)
     qemu_iovec_destroy(&iocb->iov);
     g_free(iocb->bounce);
 
-    qemu_bh_delete(iocb->bh);
-    iocb->bh = NULL;
-
     if (iocb->ret < 0) {
         block_acct_failed(stats, &iocb->acct.read);
         block_acct_failed(stats, &iocb->acct.write);
@@ -2619,7 +2614,7 @@ static void nvme_copy_bh(void *opaque)
     qemu_aio_unref(iocb);
 }
 
-static void nvme_copy_cb(void *opaque, int ret);
+static void nvme_do_copy(NvmeCopyAIOCB *iocb);
 
 static void nvme_copy_source_range_parse_format0(void *ranges, int idx,
                                                  uint64_t *slba, uint32_t *nlb,
@@ -2731,7 +2726,7 @@ static void nvme_copy_out_completed_cb(void *opaque, int ret)
     iocb->idx++;
     iocb->slba += nlb;
 out:
-    nvme_copy_cb(iocb, iocb->ret);
+    nvme_do_copy(iocb);
 }
 
 static void nvme_copy_out_cb(void *opaque, int ret)
@@ -2743,16 +2738,8 @@ static void nvme_copy_out_cb(void *opaque, int ret)
     size_t mlen;
     uint8_t *mbounce;
 
-    if (ret < 0) {
+    if (ret < 0 || iocb->ret < 0 || !ns->lbaf.ms) {
-        iocb->ret = ret;
         goto out;
-    } else if (iocb->ret < 0) {
-        goto out;
-    }
-
-    if (!ns->lbaf.ms) {
-        nvme_copy_out_completed_cb(iocb, 0);
-        return;
     }
 
     nvme_copy_source_range_parse(iocb->ranges, iocb->idx, iocb->format, NULL,
@@ -2771,7 +2758,7 @@ static void nvme_copy_out_cb(void *opaque, int ret)
     return;
 
 out:
-    nvme_copy_cb(iocb, ret);
+    nvme_copy_out_completed_cb(iocb, ret);
 }
 
 static void nvme_copy_in_completed_cb(void *opaque, int ret)
@@ -2865,15 +2852,9 @@ static void nvme_copy_in_completed_cb(void *opaque, int ret)
 
 invalid:
     req->status = status;
-    iocb->aiocb = NULL;
+    iocb->ret = -1;
-    if (iocb->bh) {
-        qemu_bh_schedule(iocb->bh);
-    }
-
-    return;
-
 out:
-    nvme_copy_cb(iocb, ret);
+    nvme_do_copy(iocb);
 }
 
 static void nvme_copy_in_cb(void *opaque, int ret)
@@ -2884,16 +2865,8 @@ static void nvme_copy_in_cb(void *opaque, int ret)
     uint64_t slba;
     uint32_t nlb;
 
-    if (ret < 0) {
+    if (ret < 0 || iocb->ret < 0 || !ns->lbaf.ms) {
-        iocb->ret = ret;
         goto out;
-    } else if (iocb->ret < 0) {
-        goto out;
-    }
-
-    if (!ns->lbaf.ms) {
-        nvme_copy_in_completed_cb(iocb, 0);
-        return;
     }
 
     nvme_copy_source_range_parse(iocb->ranges, iocb->idx, iocb->format, &slba,
@@ -2909,12 +2882,11 @@ static void nvme_copy_in_cb(void *opaque, int ret)
     return;
 
 out:
-    nvme_copy_cb(iocb, iocb->ret);
+    nvme_copy_in_completed_cb(iocb, ret);
 }
 
-static void nvme_copy_cb(void *opaque, int ret)
+static void nvme_do_copy(NvmeCopyAIOCB *iocb)
 {
-    NvmeCopyAIOCB *iocb = opaque;
     NvmeRequest *req = iocb->req;
     NvmeNamespace *ns = req->ns;
     uint64_t slba;
@@ -2922,10 +2894,7 @@ static void nvme_copy_cb(void *opaque, int ret)
     size_t len;
     uint16_t status;
 
-    if (ret < 0) {
+    if (iocb->ret < 0) {
-        iocb->ret = ret;
-        goto done;
-    } else if (iocb->ret < 0) {
         goto done;
     }
 
@@ -2972,13 +2941,10 @@ static void nvme_copy_cb(void *opaque, int ret)
 
 invalid:
     req->status = status;
+    iocb->ret = -1;
 done:
-    iocb->aiocb = NULL;
+    nvme_copy_done(iocb);
-    if (iocb->bh) {
-        qemu_bh_schedule(iocb->bh);
 }
-}
-
 
 static uint16_t nvme_copy(NvmeCtrl *n, NvmeRequest *req)
 {
@@ -3049,7 +3015,6 @@ static uint16_t nvme_copy(NvmeCtrl *n, NvmeRequest *req)
     }
 
     iocb->req = req;
-    iocb->bh = qemu_bh_new(nvme_copy_bh, iocb);
     iocb->ret = 0;
     iocb->nr = nr;
     iocb->idx = 0;
@@ -3066,7 +3031,7 @@ static uint16_t nvme_copy(NvmeCtrl *n, NvmeRequest *req)
                      BLOCK_ACCT_WRITE);
 
     req->aiocb = &iocb->common;
-    nvme_copy_cb(iocb, 0);
+    nvme_do_copy(iocb);
 
     return NVME_NO_COMPLETE;