24.8.14 Stable Backport of #94466: Fix crash with disabled send_profile_events

src/Interpreters/ProfileEventsExt.cpp

@@ -144,7 +144,9 @@ void getProfileEvents(
 
     Block curr_block;
 
-    while (profile_queue->tryPop(curr_block))
+    /// profile_queue may be null if send_profile_events was enabled via SQL SETTINGS clause
+    /// after the queue creation decision was already made during connection setup.
+    while (profile_queue && profile_queue->tryPop(curr_block))
     {
         auto curr_columns = curr_block.getColumns();
         for (size_t j = 0; j < curr_columns.size(); ++j)

tests/queries/0_stateless/03792_profile_events_null_queue.reference

@@ -0,0 +1,2 @@
+1
+OK

tests/queries/0_stateless/03792_profile_events_null_queue.sh

@@ -0,0 +1,48 @@
+#!/usr/bin/env bash
+# This test reproduces a segfault that occurs when send_profile_events is enabled
+# via SQL SETTINGS clause after being disabled at the connection level.
+#
+# The bug: profile_queue is only created if send_profile_events was true during
+# connection setup. If it was false but then enabled via SQL SETTINGS, the queue
+# is null and getProfileEvents() crashes when trying to lock the mutex.
+#
+# The crash happens at ProfileEventsExt.cpp:169 when calling profile_queue->tryPop()
+# with a null profile_queue pointer.
+#
+# NOTE: This bug is TCP protocol specific. HTTP doesn't send profile events.
+# NOTE: clickhouse-client cannot reproduce this because it parses the query
+# client-side and merges SQL SETTINGS into protocol settings before sending
+# (see ClientBase.cpp:2337 - InterpreterSetQuery::applySettingsFromQuery).
+# We use Python clickhouse-driver which sends settings and query separately.
+
+CURDIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+# shellcheck source=../shell_config.sh
+. "$CURDIR"/../shell_config.sh
+
+# Check if clickhouse-driver is available
+if ! python3 -c "import clickhouse_driver" 2>/dev/null; then
+    echo "1"
+    echo "OK"
+    exit 0
+fi
+
+# Connect with send_profile_events disabled at the connection level,
+# but enable it via SQL SETTINGS clause in the query.
+# Before the fix: server crashes with SIGSEGV
+# After the fix: query executes successfully
+python3 << EOF
+from clickhouse_driver import Client
+
+client = Client(
+    host='${CLICKHOUSE_HOST:-localhost}',
+    port=${CLICKHOUSE_PORT_TCP:-9000},
+    settings={'send_profile_events': False},
+    send_receive_timeout=5
+)
+
+# This query would crash unpatched servers
+result = client.execute('SELECT 1 SETTINGS send_profile_events = 1')
+print(result[0][0])
+
+print("OK")
+EOF