Fix lookup errors with SNI callback.

The job of an SNI callback is typically to swap out the context
associated with an SSL depending on the domain the client is trying to
talk to. Typically, only the callbacks associated with the current
context are used, but this is not the case for the SNI callback.

If SNI is run for a second time on a connection (i.e. in a
renegotiation) and the context was replaced with one that didn't itself
register an SNI callback, the old callback would run but wouldn't be
able to find its state in the context's ex data. To work around this, we
pass the pointer to the callback data directly to the callback to make
sure it's always available. It still lives in ex data to handle the
lifetime management.

Closes #979

1 files changed, 15 insertions, 7 deletions

diff --git a/openssl/src/ssl/mod.rs b/openssl/src/ssl/mod.rs
index d38063bc..f3a02c6e 100644
--- a/openssl/src/ssl/mod.rs
+++ b/openssl/src/ssl/mod.rs
@@ -658,7 +658,14 @@ impl SslContextBuilder {
         F: Fn(&mut SslRef, &mut SslAlert) -> Result<(), SniError> + 'static + Sync + Send,
     {
         unsafe {
-            self.set_ex_data(SslContext::cached_ex_index::<F>(), callback);
+            // The SNI callback is somewhat unique in that the callback associated with the original
+            // context associated with an SSL can be used even if the SSL's context has been swapped
+            // out. When that happens, we wouldn't be able to look up the callback's state in the
+            // context's ex data. Instead, pass the pointer directly as the servername arg. It's
+            // still stored in ex data to manage the lifetime.
+            let arg = self.set_ex_data_inner(SslContext::cached_ex_index::<F>(), callback);
+            ffi::SSL_CTX_set_tlsext_servername_arg(self.as_ptr(), arg);
+
             let f: extern "C" fn(_, _, _) -> _ = raw_sni::<F>;
             let f: extern "C" fn() = mem::transmute(f);
             ffi::SSL_CTX_set_tlsext_servername_callback(self.as_ptr(), Some(f));
@@ -1514,13 +1521,14 @@ impl SslContextBuilder {
     ///
     /// [`SSL_CTX_set_ex_data`]: https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_ex_data.html
     pub fn set_ex_data<T>(&mut self, index: Index<SslContext, T>, data: T) {
+        self.set_ex_data_inner(index, data);
+    }
+
+    fn set_ex_data_inner<T>(&mut self, index: Index<SslContext, T>, data: T) -> *mut c_void {
         unsafe {
-            let data = Box::new(data);
-            ffi::SSL_CTX_set_ex_data(
-                self.as_ptr(),
-                index.as_raw(),
-                Box::into_raw(data) as *mut c_void,
-            );
+            let data = Box::into_raw(Box::new(data)) as *mut c_void;
+            ffi::SSL_CTX_set_ex_data(self.as_ptr(), index.as_raw(), data);
+            data
         }
     }