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@@ -0,0 +1,56 @@
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+From c9b6668215a27f2346d5eedd6f29cc720985b448 Mon Sep 17 00:00:00 2001
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+From: Jo-Philipp Wich <jo@mein.io>
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+Date: Wed, 11 Sep 2019 21:09:59 +0200
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+Subject: [PATCH] ustream-ssl: skip writing pending data if .eof is true after
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+ connect
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+
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+Check the .eof member of the underlying ustream after the call to
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+__ustream_ssl_connect() since existing users of the library appear
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+to set the eof flag as a way to signal connection termination upon
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+failing certificate verification.
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+
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+This is a stop-gap measure to address TALOS-2019-0893 but a proper
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+API redesign is required to give applications proper control over
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+whether certificate failures are to be ignored or not and the default
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+implementation without custom callbacks should always terminate on
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+verification failures.
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+
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+Signed-off-by: Jo-Philipp Wich <jo@mein.io>
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+---
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+ ustream-ssl.c | 20 ++++++++++++++++++++
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+ 1 file changed, 20 insertions(+)
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+
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+diff --git a/ustream-ssl.c b/ustream-ssl.c
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+index e6b084b..47f66d6 100644
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+--- a/ustream-ssl.c
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++++ b/ustream-ssl.c
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+@@ -40,6 +40,26 @@ static void ustream_ssl_check_conn(struct ustream_ssl *us)
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+ return;
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+
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+ if (__ustream_ssl_connect(us) == U_SSL_OK) {
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++
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++ /* __ustream_ssl_connect() will also return U_SSL_OK when certificate
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++ * verification failed!
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++ *
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++ * Applications may register a custom .notify_verify_error callback in the
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++ * struct ustream_ssl which is called upon verification failures, but there
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++ * is no straight forward way for the callback to terminate the connection
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++ * initiation right away, e.g. through a true or false return value.
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++ *
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++ * Instead, existing implementations appear to set .eof field of the underlying
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++ * ustream in the hope that this inhibits further operations on the stream.
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++ *
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++ * Declare this informal behaviour "official" and check for the state of the
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++ * .eof member after __ustream_ssl_connect() returned, and do not write the
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++ * pending data if it is set to true.
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++ */
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++
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++ if (us->stream.eof)
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++ return;
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++
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+ us->connected = true;
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+ if (us->notify_connected)
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+ us->notify_connected(us);
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+--
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+2.20.1
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+
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Jo-Philipp Wich