[PATCH] hw/arm/smmuv3-accel: Fix veventq read returning true on EAGAIN/EINTR

[Shameer Kolothum]

smmuv3_accel_event_read_validate() returns true for EAGAIN/EINTR, but
no data has been read into the buffer. Callers treat true as success and
proceed to use the uninitialized buffer. Return false instead and guard
warn_report_err_once() against NULL Error in both callers.

Resolves: Coverity CID 1660057
Fixes: d4aea0f75b ("hw/arm/smmuv3-accel: Introduce common helper for veventq 
read")
Reported-by: Peter Maydell <peter.mayd...@linaro.org>
Signed-off-by: Shameer Kolothum <skolothum...@nvidia.com>
---
 hw/arm/smmuv3-accel.c   | 6 ++++--
 hw/arm/tegra241-cmdqv.c | 4 +++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
index 80900c2521..6d402d2ba6 100644
--- a/hw/arm/smmuv3-accel.c
+++ b/hw/arm/smmuv3-accel.c
@@ -451,7 +451,7 @@ bool smmuv3_accel_event_read_validate(IOMMUFDVeventq 
*veventq, uint32_t type,
     bytes = read(veventq->veventq_fd, buf, size);
     if (bytes <= 0) {
         if (errno == EAGAIN || errno == EINTR) {
-            return true;
+            return false;
         }
         error_setg(errp, "vEVENTQ(type %u id %u): read failed (%m)", type, id);
         return false;
@@ -491,7 +491,9 @@ static void smmuv3_accel_event_read(void *opaque)
     if (!smmuv3_accel_event_read_validate(veventq,
                                           IOMMU_VEVENTQ_TYPE_ARM_SMMUV3, &buf,
                                           sizeof(buf), &local_err)) {
-        warn_report_err_once(local_err);
+        if (local_err) {
+            warn_report_err_once(local_err);
+        }
         return;
     }
     smmuv3_propagate_event(s, (Evt *)&buf.vevent);
diff --git a/hw/arm/tegra241-cmdqv.c b/hw/arm/tegra241-cmdqv.c
index 29c488e0e4..bb0b417e90 100644
--- a/hw/arm/tegra241-cmdqv.c
+++ b/hw/arm/tegra241-cmdqv.c
@@ -845,7 +845,9 @@ static void tegra241_cmdqv_event_read(void *opaque)
     if (!smmuv3_accel_event_read_validate(veventq,
                                           IOMMU_VEVENTQ_TYPE_TEGRA241_CMDQV,
                                           &buf, sizeof(buf), &local_err)) {
-        warn_report_err_once(local_err);
+        if (local_err) {
+            warn_report_err_once(local_err);
+        }
         return;
     }
 
-- 
2.43.0