fix lint-6 tests and add readme

lints/duplicate-mutable-accounts/README.md

@@ -0,0 +1,47 @@
+# duplicate_mutable_accounts
+
+**What it does:** Checks to make sure there is a key check on identical Anchor accounts.
+The key check serves to make sure that two identical accounts do not have the same key,
+ie, they are unique. An Anchor account (`Account<'info, T>`) is identical to another if 
+the generic parameter `T` is the same type for each account.
+
+**Why is this bad?** If a program contains two identical, mutable Anchor accounts, and
+performs some operation on those accounts, then a user could pass in the same account
+twice. Then any previous operations may be overwritten by the last operation, which may
+not be what the program wanted if it expected different accounts.
+
+**Known problems:** If a program is not using the anchor `#[account]` macro constraints,
+and is instead using checks in the function bodies, and the program uses boolean operator
+&& or || to link constraints in a single if statement, the lint will flag this as a false
+positive since the lint only catches statements with `==` or `!=`.
+
+Another issue is if a program uses an if statement such as `a.key() == b.key()` and then
+continues to modify the accounts, then this will not be caught. The reason is because the
+lint regards expressions with `==` as a secure check, since it assumes the program will
+then return an error (see the secure example). However, it does not explicitly check that
+an error is returned.
+
+In general, this lint will catch all vulnerabilities if the anchor macro constraints are
+used (see the recommended example). It is not as robust if alternative methods are utilized.
+Thus it is encouraged to use the anchor `#[account]` macro constraints.
+
+**Example:**
+
+```rust
+#[derive(Accounts)]
+pub struct Update<'info> {
+    user_a: Account<'info, User>,
+    user_b: Account<'info, User>,
+}
+```
+
+Use instead:
+
+```rust
+#[derive(Accounts)]
+pub struct Update<'info> {
+    #[account(constraint = user_a.key() != user_b.key())]
+    user_a: Account<'info, User>,
+    user_b: Account<'info, User>,
+}
+```

lints/duplicate-mutable-accounts/src/lib.rs

@@ -27,24 +27,51 @@ use solana_lints::paths;
 const ANCHOR_ACCOUNT_GENERIC_ARG_COUNT: usize = 2;
 
 dylint_linting::impl_late_lint! {
-    /// **What it does:**
+    /// **What it does:** Checks to make sure there is a key check on identical Anchor accounts.
+    /// The key check serves to make sure that two identical accounts do not have the same key,
+    /// ie, they are unique. An Anchor account (`Account<'info, T>`) is identical to another if 
+    /// the generic parameter `T` is the same type for each account.
     ///
-    /// **Why is this bad?**
+    /// **Why is this bad?** If a program contains two identical, mutable Anchor accounts, and
+    /// performs some operation on those accounts, then a user could pass in the same account
+    /// twice. Then any previous operations may be overwritten by the last operation, which may
+    /// not be what the program wanted if it expected different accounts.
     ///
-    /// **Known problems:** None.
+    /// **Known problems:** If a program is not using the anchor #[account] macro constraints,
+    /// and is instead using checks in the function bodies, and the program uses boolean operator
+    /// && or || to link constraints in a single if statement, the lint will flag this as a false
+    /// positive since the lint only catches statements with `==` or `!=`.
+    /// Another issue is if a program uses an if statement such as `a.key() == b.key()` and then
+    /// continues to modify the accounts, then this will not be caught. The reason is because the
+    /// lint regards expressions with `==` as a secure check, since it assumes the program will
+    /// then return an error (see the secure example). However, it does not explicitly check that
+    /// an error is returned.
+    /// 
+    /// In general, this lint will catch all vulnerabilities if the anchor macro constraints are
+    /// used (see the recommended example). It is not as robust if alternative methods are utilized.
+    /// Thus it is encouraged to use the anchor `#[account]` macro constraints.
     ///
-    /// **Example:**
+    /// **Example:** 
     ///
     /// ```rust
-    /// // example code where a warning is issued
+    /// #[derive(Accounts)]
+    /// pub struct Update<'info> {
+    ///     user_a: Account<'info, User>,
+    ///     user_b: Account<'info, User>,
+    /// }
     /// ```
     /// Use instead:
     /// ```rust
-    /// // example code that does not raise a warning
+    /// #[derive(Accounts)]
+    /// pub struct Update<'info> {
+    ///     #[account(constraint = user_a.key() != user_b.key())]
+    ///     user_a: Account<'info, User>,
+    ///     user_b: Account<'info, User>,
+    /// }
     /// ```
     pub DUPLICATE_MUTABLE_ACCOUNTS,
     Warn,
-    "description goes here",
+    "does not check if multiple identical Anchor accounts have different keys",
     DuplicateMutableAccounts::default()
 }
 
@@ -156,7 +183,7 @@ impl<'tcx> LateLintPass<'tcx> for DuplicateMutableAccounts {
                     cx,
                     DUPLICATE_MUTABLE_ACCOUNTS,
                     *first,
-                    "the following expressions have equivalent Account types, yet do not contain a proper key check.",
+                    &format!("the expressions on line {:?} and {:?} have identical Account types, yet do not contain a proper key check.", first, second),
                     Some(*second),
                     "add a key check to make sure the accounts have different keys, e.g., x.key() != y.key()",
                 );

lints/duplicate-mutable-accounts/ui/insecure-2/src/lib.rs

@@ -10,12 +10,15 @@ pub mod duplicate_mutable_accounts_insecure {
         ctx: Context<Update>,
         a: u64,
         b: u64,
+        c: u64,
     ) -> anchor_lang::solana_program::entrypoint::ProgramResult {
         let user_a = &mut ctx.accounts.user_a;
         let user_b = &mut ctx.accounts.user_b;
+        let user_c = &mut ctx.accounts.user_c;
 
         user_a.data = a;
         user_b.data = b;
+        user_c.data = c;
         Ok(())
     }
 }

lints/duplicate-mutable-accounts/ui/insecure-2/src/lib.stderr

@@ -1,39 +1,39 @@
-error: user_a and user_b have identical account types but do not have a key check constraint
-  --> $DIR/lib.rs:25:5
+error: the expressions on line $DIR/lib.rs:15:27: 15:46 (#0) and $DIR/lib.rs:16:27: 16:46 (#0) have identical Account types, yet do not contain a proper key check.
+  --> $DIR/lib.rs:15:27
    |
-LL |     user_a: Account<'info, User>,
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let user_a = &mut ctx.accounts.user_a;
+   |                           ^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D duplicate-mutable-accounts` implied by `-D warnings`
-help: add an anchor key check constraint: #[account(constraint = user_a.key() != user_b.key())]
-  --> $DIR/lib.rs:26:5
+help: add a key check to make sure the accounts have different keys, e.g., x.key() != y.key()
+  --> $DIR/lib.rs:16:27
    |
-LL |     user_b: Account<'info, User>,
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let user_b = &mut ctx.accounts.user_b;
+   |                           ^^^^^^^^^^^^^^^^^^^
 
-error: user_a and user_c have identical account types but do not have a key check constraint
-  --> $DIR/lib.rs:25:5
+error: the expressions on line $DIR/lib.rs:15:27: 15:46 (#0) and $DIR/lib.rs:17:27: 17:46 (#0) have identical Account types, yet do not contain a proper key check.
+  --> $DIR/lib.rs:15:27
    |
-LL |     user_a: Account<'info, User>,
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let user_a = &mut ctx.accounts.user_a;
+   |                           ^^^^^^^^^^^^^^^^^^^
    |
-help: add an anchor key check constraint: #[account(constraint = user_a.key() != user_c.key())]
-  --> $DIR/lib.rs:27:5
+help: add a key check to make sure the accounts have different keys, e.g., x.key() != y.key()
+  --> $DIR/lib.rs:17:27
    |
-LL |     user_c: Account<'info, User>,
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let user_c = &mut ctx.accounts.user_c;
+   |                           ^^^^^^^^^^^^^^^^^^^
 
-error: user_b and user_c have identical account types but do not have a key check constraint
-  --> $DIR/lib.rs:26:5
+error: the expressions on line $DIR/lib.rs:16:27: 16:46 (#0) and $DIR/lib.rs:17:27: 17:46 (#0) have identical Account types, yet do not contain a proper key check.
+  --> $DIR/lib.rs:16:27
    |
-LL |     user_b: Account<'info, User>,
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let user_b = &mut ctx.accounts.user_b;
+   |                           ^^^^^^^^^^^^^^^^^^^
    |
-help: add an anchor key check constraint: #[account(constraint = user_b.key() != user_c.key())]
-  --> $DIR/lib.rs:27:5
+help: add a key check to make sure the accounts have different keys, e.g., x.key() != y.key()
+  --> $DIR/lib.rs:17:27
    |
-LL |     user_c: Account<'info, User>,
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let user_c = &mut ctx.accounts.user_c;
+   |                           ^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 3 previous errors
 

lints/duplicate-mutable-accounts/ui/insecure/src/lib.stderr

@@ -1,15 +1,15 @@
-error: user_a and user_b have identical account types but do not have a key check constraint
-  --> $DIR/lib.rs:25:5
+error: the expressions on line $DIR/lib.rs:14:27: 14:46 (#0) and $DIR/lib.rs:15:27: 15:46 (#0) have identical Account types, yet do not contain a proper key check.
+  --> $DIR/lib.rs:14:27
    |
-LL |     user_a: Account<'info, User>,
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let user_a = &mut ctx.accounts.user_a;
+   |                           ^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D duplicate-mutable-accounts` implied by `-D warnings`
-help: add an anchor key check constraint: #[account(constraint = user_a.key() != user_b.key())]
-  --> $DIR/lib.rs:26:5
+help: add a key check to make sure the accounts have different keys, e.g., x.key() != y.key()
+  --> $DIR/lib.rs:15:27
    |
-LL |     user_b: Account<'info, User>,
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let user_b = &mut ctx.accounts.user_b;
+   |                           ^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to previous error