[tarantool-patches] [PATCH] sql: decrease max depth of expression AST

[Nikita Pettik <korablev@tarantool.org>]

Currently, all routines connected with expression AST processing rely on
recursive approaches. On the other hand, SQL is executed in a standard
fiber, which features only 64kb of stack memory. Hence, deep recursion
can result in stack overflow. To avoid obvious overflows lets
significantly restrict allowed depth of expression AST. Note that it is
not radical solution to this problem but rather temporary fix.

Workaround for #3861
---
Branch: https://github.com/tarantool/tarantool/tree/np/gh-3861-reduce-expr-AST-depth
Issue: https://github.com/tarantool/tarantool/issues/3861

 src/box/sql/sqliteLimit.h    |  2 +-
 test/sql-tap/where7.test.lua | 32 ++++++++++++++++++++++----------
 2 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/src/box/sql/sqliteLimit.h b/src/box/sql/sqliteLimit.h
index 3b474ed9f..e7d1b63c2 100644
--- a/src/box/sql/sqliteLimit.h
+++ b/src/box/sql/sqliteLimit.h
@@ -106,7 +106,7 @@ enum {
  * at all times.
  */
 #ifndef SQLITE_MAX_EXPR_DEPTH
-#define SQLITE_MAX_EXPR_DEPTH 1000
+#define SQLITE_MAX_EXPR_DEPTH 200
 #endif
 
 /*
diff --git a/test/sql-tap/where7.test.lua b/test/sql-tap/where7.test.lua
index 09cbe53d1..d5f389347 100755
--- a/test/sql-tap/where7.test.lua
+++ b/test/sql-tap/where7.test.lua
@@ -1,6 +1,6 @@
 #!/usr/bin/env tarantool
 test = require("sqltester")
-test:plan(2022)
+test:plan(2023)
 
 --!./tcltestrunner.lua
 -- 2008 December 23
@@ -230,14 +230,14 @@ test:do_test(
     "where7-1.20",
     function()
         sql = "SELECT a FROM t1 WHERE a=11 OR b=11"
-        for i = 12, 400 - 1, 1 do
+        for i = 12, 100 do
             sql = sql .. string.format(" OR a=%s OR b=%s", i, i)
         end
         sql = sql .. " ORDER BY a"
         return count_steps(sql)
     end, {
         -- <where7-1.20>
-        
+
         -- </where7-1.20>
     })
 
@@ -245,7 +245,7 @@ test:do_test(
     "where7-1.21",
     function()
         sql = "SELECT a FROM t1 WHERE b=11 OR c=11"
-        for i = 12, 400 - 1, 1 do
+        for i = 12, 100 do
             sql = sql .. string.format(" OR b=%s OR c=%s", i, i)
         end
         sql = sql .. " ORDER BY a"
@@ -260,7 +260,7 @@ test:do_test(
     "where7-1.22",
     function()
         sql = "SELECT a FROM t1 WHERE (b=11 OR c=11"
-        for i = 12, 400 - 1, 1 do
+        for i = 12, 100 do
             sql = sql .. string.format(" OR b=%s OR c=%s", i, i)
         end
         sql = sql .. ") AND d>=0 AND d<9999 ORDER BY a"
@@ -275,7 +275,7 @@ test:do_test(
     "where7-1.23",
     function()
         sql = "SELECT a FROM t1 WHERE (b=11 OR c=11"
-        for i = 12, 400 - 1, 1 do
+        for i = 12, 100 do
             sql = sql .. string.format(" OR (b=%s AND d!=0) OR (c=%s AND d IS NOT NULL)", i, i)
         end
         sql = sql .. ") AND d>=0 AND d<9999 ORDER BY a"
@@ -290,14 +290,14 @@ test:do_test(
     "where7-1.31",
     function()
         sql = "SELECT a FROM t1 WHERE (a=11 AND b=11)"
-        for i = 12, 400 - 1, 1 do
+        for i = 12, 100 do
             sql = sql .. string.format(" OR (a=%s AND b=%s)", i, i)
         end
         sql = sql .. " ORDER BY a"
         return count_steps(sql)
     end, {
         -- <where7-1.31>
-        
+
         -- </where7-1.31>
     })
 
@@ -305,17 +305,29 @@ test:do_test(
     "where7-1.32",
     function()
         sql = "SELECT a FROM t1 WHERE (b=11 AND c=11)"
-        for i = 12, 400 - 1, 1 do
+        for i = 12, 100 do
             sql = sql .. string.format(" OR (b=%s AND c=%s)", i, i)
         end
         sql = sql .. " ORDER BY a"
         return count_steps(sql)
     end, {
         -- <where7-1.32>
-        
+
         -- </where7-1.32>
     })
 
+test:do_test(
+    "where7-AST-depth-limit",
+    function()
+        sql = "SELECT a FROM t1 WHERE a = 0"
+        for i = 1, 199 do
+            sql = sql .. string.format(" OR a = %s", i)
+        end
+        return test:catchsql(sql)
+    end, {
+        1, "Expression tree is too large (maximum depth 200)"
+    })
+
 test:do_test(
     "where7-2.1",
     function()
-- 
2.15.1