drm: Validate conn before dereference in CDRMAtomicRequest::commit() (#108)

During startup, CDRMAtomicImpl::reset() may emit a call to method
commit of a CDRMAtomicRequest instance with member "conn" uninitialized,
leading to a segfault. Validate the the pointer before dereference it as
a workaround.

Fixes: 55ac962 ("DRM: preliminary atomic support")
Closes: #107

Signed-off-by: Yao Zi <[email protected]>

Author: ziyao233

src/backend/drm/impl/Atomic.cpp

@@ -162,6 +162,9 @@ bool Aquamarine::CDRMAtomicRequest::commit(uint32_t flagssss) {
         return false;
     }
 
+    if (!conn)
+        return false;
+
     if (auto ret = drmModeAtomicCommit(backend->gpu->fd, req, flagssss, &conn->pendingPageFlip); ret) {
         backend->log((flagssss & DRM_MODE_ATOMIC_TEST_ONLY) ? AQ_LOG_DEBUG : AQ_LOG_ERROR,
                      std::format("atomic drm request: failed to commit: {}, flags: {}", strerror(-ret), flagsToStr(flagssss)));
@@ -365,4 +368,4 @@ bool Aquamarine::CDRMAtomicImpl::moveCursor(SP<SDRMConnector> connector, bool sk
     }
 
     return true;
-}
+}