Add configurable recursion limit to parser, to protect against stack …

…overflows (#764)

src/lib.rs

@@ -12,11 +12,15 @@
 
 //! SQL Parser for Rust
 //!
-//! Example code:
-//!
 //! This crate provides an ANSI:SQL 2011 lexer and parser that can parse SQL
 //! into an Abstract Syntax Tree (AST).
 //!
+//! See [`Parser::parse_sql`](crate::parser::Parser::parse_sql) and
+//! [`Parser::new`](crate::parser::Parser::new) for the Parsing API
+//! and the [`ast`](crate::ast) crate for the AST structure.
+//!
+//! Example:
+//!
 //! ```
 //! use sqlparser::dialect::GenericDialect;
 //! use sqlparser::parser::Parser;

src/parser.rs

@@ -37,6 +37,7 @@ use crate::tokenizer::*;
 pub enum ParserError {
     TokenizerError(String),
     ParserError(String),
+    RecursionLimitExceeded,
 }
 
 // Use `Parser::expected` instead, if possible
@@ -55,6 +56,92 @@ macro_rules! return_ok_if_some {
     }};
 }
 
+#[cfg(feature = "std")]
+/// Implemenation [`RecursionCounter`] if std is available
+mod recursion {
+    use core::sync::atomic::{AtomicUsize, Ordering};
+    use std::rc::Rc;
+
+    use super::ParserError;
+
+    /// Tracks remaining recursion depth. This value is decremented on
+    /// each call to `try_decrease()`, when it reaches 0 an error will
+    /// be returned.
+    ///
+    /// Note: Uses an Rc and AtomicUsize in order to satisfy the Rust
+    /// borrow checker so the automatic DepthGuard decrement a
+    /// reference to the counter. The actual value is not modified
+    /// concurrently
+    pub(crate) struct RecursionCounter {
+        remaining_depth: Rc<AtomicUsize>,
+    }
+
+    impl RecursionCounter {
+        /// Creates a [`RecursionCounter`] with the specified maximum
+        /// depth
+        pub fn new(remaining_depth: usize) -> Self {
+            Self {
+                remaining_depth: Rc::new(remaining_depth.into()),
+            }
+        }
+
+        /// Decreases the remaining depth by 1.
+        ///
+        /// Returns `Err` if the remaining depth falls to 0.
+        ///
+        /// Returns a [`DepthGuard`] which will adds 1 to the
+        /// remaining depth upon drop;
+        pub fn try_decrease(&self) -> Result<DepthGuard, ParserError> {
+            let old_value = self.remaining_depth.fetch_sub(1, Ordering::SeqCst);
+            // ran out of space
+            if old_value == 0 {
+                Err(ParserError::RecursionLimitExceeded)
+            } else {
+                Ok(DepthGuard::new(Rc::clone(&self.remaining_depth)))
+            }
+        }
+    }
+
+    /// Guard that increass the remaining depth by 1 on drop
+    pub struct DepthGuard {
+        remaining_depth: Rc<AtomicUsize>,
+    }
+
+    impl DepthGuard {
+        fn new(remaining_depth: Rc<AtomicUsize>) -> Self {
+            Self { remaining_depth }
+        }
+    }
+    impl Drop for DepthGuard {
+        fn drop(&mut self) {
+            self.remaining_depth.fetch_add(1, Ordering::SeqCst);
+        }
+    }
+}
+
+#[cfg(not(feature = "std"))]
+mod recursion {
+    /// Implemenation [`RecursionCounter`] if std is NOT available (and does not
+    /// guard against stack overflow).
+    ///
+    /// Has the same API as the std RecursionCounter implementation
+    /// but does not actually limit stack depth.
+    pub(crate) struct RecursionCounter {}
+
+    impl RecursionCounter {
+        pub fn new(_remaining_depth: usize) -> Self {
+            Self {}
+        }
+        pub fn try_decrease(&self) -> Result<DepthGuard, super::ParserError> {
+            Ok(DepthGuard {})
+        }
+    }
+
+    pub struct DepthGuard {}
+}
+
+use recursion::RecursionCounter;
+
 #[derive(PartialEq, Eq)]
 pub enum IsOptional {
     Optional,
@@ -96,6 +183,7 @@ impl fmt::Display for ParserError {
             match self {
                 ParserError::TokenizerError(s) => s,
                 ParserError::ParserError(s) => s,
+                ParserError::RecursionLimitExceeded => "recursion limit exceeded",
             }
         )
     }
@@ -104,22 +192,78 @@ impl fmt::Display for ParserError {
 #[cfg(feature = "std")]
 impl std::error::Error for ParserError {}
 
+// By default, allow expressions up to this deep before erroring
+const DEFAULT_REMAINING_DEPTH: usize = 50;
+
 pub struct Parser<'a> {
     tokens: Vec<TokenWithLocation>,
     /// The index of the first unprocessed token in `self.tokens`
     index: usize,
+    /// The current dialect to use
     dialect: &'a dyn Dialect,
+    /// ensure the stack does not overflow by limiting recusion depth
+    recursion_counter: RecursionCounter,
 }
 
 impl<'a> Parser<'a> {
-    /// Parse the specified tokens
-    /// To avoid breaking backwards compatibility, this function accepts
-    /// bare tokens.
-    pub fn new(tokens: Vec<Token>, dialect: &'a dyn Dialect) -> Self {
-        Parser::new_without_locations(tokens, dialect)
+    /// Create a parser for a [`Dialect`]
+    ///
+    /// See also [`Parser::parse_sql`]
+    ///
+    /// Example:
+    /// ```
+    /// # use sqlparser::{parser::{Parser, ParserError}, dialect::GenericDialect};
+    /// # fn main() -> Result<(), ParserError> {
+    /// let dialect = GenericDialect{};
+    /// let statements = Parser::new(&dialect)
+    ///   .try_with_sql("SELECT * FROM foo")?
+    ///   .parse_statements()?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn new(dialect: &'a dyn Dialect) -> Self {
+        Self {
+            tokens: vec![],
+            index: 0,
+            dialect,
+            recursion_counter: RecursionCounter::new(DEFAULT_REMAINING_DEPTH),
+        }
+    }
+
+    /// Specify the maximum recursion limit while parsing.
+    ///
+    ///
+    /// [`Parser`] prevents stack overflows by returning
+    /// [`ParserError::RecursionLimitExceeded`] if the parser exceeds
+    /// this depth while processing the query.
+    ///
+    /// Example:
+    /// ```
+    /// # use sqlparser::{parser::{Parser, ParserError}, dialect::GenericDialect};
+    /// # fn main() -> Result<(), ParserError> {
+    /// let dialect = GenericDialect{};
+    /// let result = Parser::new(&dialect)
+    ///   .with_recursion_limit(1)
+    ///   .try_with_sql("SELECT * FROM foo WHERE (a OR (b OR (c OR d)))")?
+    ///   .parse_statements();
+    ///   assert_eq!(result, Err(ParserError::RecursionLimitExceeded));
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn with_recursion_limit(mut self, recursion_limit: usize) -> Self {
+        self.recursion_counter = RecursionCounter::new(recursion_limit);
+        self
+    }
+
+    /// Reset this parser to parse the specified token stream
+    pub fn with_tokens_with_locations(mut self, tokens: Vec<TokenWithLocation>) -> Self {
+        self.tokens = tokens;
+        self.index = 0;
+        self
     }
 
-    pub fn new_without_locations(tokens: Vec<Token>, dialect: &'a dyn Dialect) -> Self {
+    /// Reset this parser state to parse the specified tokens
+    pub fn with_tokens(self, tokens: Vec<Token>) -> Self {
         // Put in dummy locations
         let tokens_with_locations: Vec<TokenWithLocation> = tokens
             .into_iter()
@@ -128,49 +272,84 @@ impl<'a> Parser<'a> {
                 location: Location { line: 0, column: 0 },
             })
             .collect();
-        Parser::new_with_locations(tokens_with_locations, dialect)
+        self.with_tokens_with_locations(tokens_with_locations)
     }
 
-    /// Parse the specified tokens
-    pub fn new_with_locations(tokens: Vec<TokenWithLocation>, dialect: &'a dyn Dialect) -> Self {
-        Parser {
-            tokens,
-            index: 0,
-            dialect,
-        }
+    /// Tokenize the sql string and sets this [`Parser`]'s state to
+    /// parse the resulting tokens
+    ///
+    /// Returns an error if there was an error tokenizing the SQL string.
+    ///
+    /// See example on [`Parser::new()`] for an example
+    pub fn try_with_sql(self, sql: &str) -> Result<Self, ParserError> {
+        debug!("Parsing sql '{}'...", sql);
+        let mut tokenizer = Tokenizer::new(self.dialect, sql);
+        let tokens = tokenizer.tokenize()?;
+        Ok(self.with_tokens(tokens))
     }
 
-    /// Parse a SQL statement and produce an Abstract Syntax Tree (AST)
-    pub fn parse_sql(dialect: &dyn Dialect, sql: &str) -> Result<Vec<Statement>, ParserError> {
-        let mut tokenizer = Tokenizer::new(dialect, sql);
-        let tokens = tokenizer.tokenize()?;
-        let mut parser = Parser::new(tokens, dialect);
+    /// Parse potentially multiple statements
+    ///
+    /// Example
+    /// ```
+    /// # use sqlparser::{parser::{Parser, ParserError}, dialect::GenericDialect};
+    /// # fn main() -> Result<(), ParserError> {
+    /// let dialect = GenericDialect{};
+    /// let statements = Parser::new(&dialect)
+    ///   // Parse a SQL string with 2 separate statements
+    ///   .try_with_sql("SELECT * FROM foo; SELECT * FROM bar;")?
+    ///   .parse_statements()?;
+    /// assert_eq!(statements.len(), 2);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn parse_statements(&mut self) -> Result<Vec<Statement>, ParserError> {
         let mut stmts = Vec::new();
         let mut expecting_statement_delimiter = false;
-        debug!("Parsing sql '{}'...", sql);
         loop {
             // ignore empty statements (between successive statement delimiters)
-            while parser.consume_token(&Token::SemiColon) {
+            while self.consume_token(&Token::SemiColon) {
                 expecting_statement_delimiter = false;
             }
 
-            if parser.peek_token() == Token::EOF {
+            if self.peek_token() == Token::EOF {
                 break;
             }
             if expecting_statement_delimiter {
-                return parser.expected("end of statement", parser.peek_token());
+                return self.expected("end of statement", self.peek_token());
             }
 
-            let statement = parser.parse_statement()?;
+            let statement = self.parse_statement()?;
             stmts.push(statement);
             expecting_statement_delimiter = true;
         }
         Ok(stmts)
     }
 
+    /// Convience method to parse a string with one or more SQL
+    /// statements into produce an Abstract Syntax Tree (AST).
+    ///
+    /// Example
+    /// ```
+    /// # use sqlparser::{parser::{Parser, ParserError}, dialect::GenericDialect};
+    /// # fn main() -> Result<(), ParserError> {
+    /// let dialect = GenericDialect{};
+    /// let statements = Parser::parse_sql(
+    ///   &dialect, "SELECT * FROM foo"
+    /// )?;
+    /// assert_eq!(statements.len(), 1);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn parse_sql(dialect: &dyn Dialect, sql: &str) -> Result<Vec<Statement>, ParserError> {
+        Parser::new(dialect).try_with_sql(sql)?.parse_statements()
+    }
+
     /// Parse a single top-level statement (such as SELECT, INSERT, CREATE, etc.),
     /// stopping before the statement separator, if any.
     pub fn parse_statement(&mut self) -> Result<Statement, ParserError> {
+        let _guard = self.recursion_counter.try_decrease()?;
+
         // allow the dialect to override statement parsing
         if let Some(statement) = self.dialect.parse_statement(self) {
             return statement;
@@ -364,6 +543,7 @@ impl<'a> Parser<'a> {
 
     /// Parse a new expression
     pub fn parse_expr(&mut self) -> Result<Expr, ParserError> {
+        let _guard = self.recursion_counter.try_decrease()?;
         self.parse_subexpr(0)
     }
 
@@ -4512,6 +4692,7 @@ impl<'a> Parser<'a> {
     /// by `ORDER BY`. Unlike some other parse_... methods, this one doesn't
     /// expect the initial keyword to be already consumed
     pub fn parse_query(&mut self) -> Result<Query, ParserError> {
+        let _guard = self.recursion_counter.try_decrease()?;
         let with = if self.parse_keyword(Keyword::WITH) {
             Some(With {
                 recursive: self.parse_keyword(Keyword::RECURSIVE),

src/test_utils.rs

@@ -29,7 +29,6 @@ use core::fmt::Debug;
 use crate::ast::*;
 use crate::dialect::*;
 use crate::parser::{Parser, ParserError};
-use crate::tokenizer::Tokenizer;
 
 /// Tests use the methods on this struct to invoke the parser on one or
 /// multiple dialects.
@@ -65,9 +64,8 @@ impl TestedDialects {
         F: Fn(&mut Parser) -> T,
     {
         self.one_of_identical_results(|dialect| {
-            let mut tokenizer = Tokenizer::new(dialect, sql);
-            let tokens = tokenizer.tokenize().unwrap();
-            f(&mut Parser::new(tokens, dialect))
+            let mut parser = Parser::new(dialect).try_with_sql(sql).unwrap();
+            f(&mut parser)
         })
     }