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Feature #13245

open

[PATCH] reject inter-thread TLS modification

Added by shyouhei (Shyouhei Urabe) almost 5 years ago. Updated about 4 years ago.

Status:
Open
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:79715]

Description

Thread local and fiber local storages are by nature expected to be
visible from within the thread / fiber and not from anywhere else. OK?

That's a hoax.

The truth is they are visible from anywhere. Thread local variable
for instance is just a set of key-value pair that is stored inside of
a thread instance variable. No access control is ever attempted since
the beginning. So you can touch any thread's any local storages at
will at any time without any synchronization.

This embarrasing "feature" has been there for a long time. I thinnk
it's too late to remove the TLS accessor methods because they are used
everywhere. BUT, even with that assumption, I strongly believe that
tampering other thread's local storage is something you must not.

Preventing such access should harm no one.

Signed-off-by: Urabe, Shyouhei shyouhei@ruby-lang.org

---
 test/ruby/test_fiber.rb  | 7 +++++++
 test/ruby/test_thread.rb | 7 +++++++
 thread.c                 | 8 ++++++++
 3 files changed, 22 insertions(+)

diff --git a/test/ruby/test_fiber.rb b/test/ruby/test_fiber.rb
index d1d15828fc..319de9e7b2 100644
--- a/test/ruby/test_fiber.rb
+++ b/test/ruby/test_fiber.rb
@@ -169,6 +169,13 @@ def tvar(var, val)
     assert_equal(nil, Thread.current[:v]);
   end

+  def test_inter_thread_tls
+    t = Thread.new { }
+    assert_raise(ThreadError) do
+      t[:foo] = "bar"
+    end
+  end
+
   def test_alive
     fib = Fiber.new{Fiber.yield}
     assert_equal(true, fib.alive?)
diff --git a/test/ruby/test_thread.rb b/test/ruby/test_thread.rb
index c82018dc8e..5ad663becf 100644
--- a/test/ruby/test_thread.rb
+++ b/test/ruby/test_thread.rb
@@ -95,6 +95,13 @@ def test_thread_variable_frozen
     end
   end

+  def test_inter_thread_variable
+    t = Thread.new { }
+    assert_raise(ThreadError) do
+      t.thread_variable_set(:foo, "bar")
+    end
+  end
+
   def test_mutex_synchronize
     m = Thread::Mutex.new
     r = 0
diff --git a/thread.c b/thread.c
index 597fd293d6..03f7777aae 100644
--- a/thread.c
+++ b/thread.c
@@ -3154,6 +3154,10 @@ rb_thread_local_aset(VALUE thread, ID id, VALUE val)
    rb_error_frozen("thread locals");
     }

+    if (th != GET_THREAD()) {
+        rb_raise(rb_eThreadError, "inter-thread access of TLS prohibited");
+    }
+
     return threadptr_local_aset(th, id, val);
 }

@@ -3231,6 +3235,10 @@ rb_thread_variable_set(VALUE thread, VALUE id, VALUE val)
    rb_error_frozen("thread locals");
     }

+    if (thread != GET_THREAD()->self) {
+        rb_raise(rb_eThreadError, "inter-thread access of TLS prohibited");
+    }
+
     locals = rb_ivar_get(thread, id_locals);
     return rb_hash_aset(locals, rb_to_symbol(id), val);
 }
-- 
2.11.1
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