Re: [PATCH v2 1/3] io/crypto: Move tls premature termination handling into QIO layer

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Sep 11, 2025 at 05:23:53PM -0400, Peter Xu wrote:
> QCryptoTLSSession allows TLS premature termination in two cases, one of the
> case is when the channel shutdown() is invoked on READ side.
> 
> It's possible the shutdown() happened after the read thread blocked at
> gnutls_record_recv().  In this case, we should allow the premature
> termination to happen.
> 
> The problem is by the time qcrypto_tls_session_read() was invoked,
> tioc->shutdown may not have been set, so this may instead be treated as an
> error if there is concurrent shutdown() calls.
> 
> To allow the flag to reflect the latest status of tioc->shutdown, move the
> check upper into the QIOChannel level, so as to read the flag only after
> QEMU gets an GNUTLS_E_PREMATURE_TERMINATION.
> 
> When at it, introduce qio_channel_tls_allow_premature_termination() helper
> to make the condition checks easier to read.
> 
> This patch will fix a qemu qtest warning when running the preempt tls test,
> reporting premature termination:
> 
> QTEST_QEMU_BINARY=./qemu-system-x86_64 ./tests/qtest/migration-test --full -r /x86_64/migration/postcopy/preempt/tls/psk
> ...
> qemu-kvm: Cannot read from TLS channel: The TLS connection was non-properly terminated.
> ...
> 
> In this specific case, the error was set by postcopy_preempt_thread, which
> normally will be concurrently shutdown()ed by the main thread.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  include/crypto/tlssession.h |  7 +------
>  crypto/tlssession.c         |  7 ++-----
>  io/channel-tls.c            | 21 +++++++++++++++++++--
>  3 files changed, 22 insertions(+), 13 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

> diff --git a/include/crypto/tlssession.h b/include/crypto/tlssession.h
> index 2f62ce2d67..6b4fcadee7 100644
> --- a/include/crypto/tlssession.h
> +++ b/include/crypto/tlssession.h
> @@ -110,6 +110,7 @@
>  typedef struct QCryptoTLSSession QCryptoTLSSession;
>  
>  #define QCRYPTO_TLS_SESSION_ERR_BLOCK -2
> +#define QCRYPTO_TLS_SESSION_PREMATURE_TERMINATION -3
>  
>  /**
>   * qcrypto_tls_session_new:
> @@ -259,7 +260,6 @@ ssize_t qcrypto_tls_session_write(QCryptoTLSSession *sess,
>   * @sess: the TLS session object
>   * @buf: to fill with plain text received
>   * @len: the length of @buf
> - * @gracefulTermination: treat premature termination as graceful EOF
>   * @errp: pointer to hold returned error object
>   *
>   * Receive up to @len bytes of data from the remote peer
> @@ -267,10 +267,6 @@ ssize_t qcrypto_tls_session_write(QCryptoTLSSession *sess,
>   * qcrypto_tls_session_set_callbacks(), decrypt it and
>   * store it in @buf.
>   *
> - * If @gracefulTermination is true, then a premature termination
> - * of the TLS session will be treated as indicating EOF, as
> - * opposed to an error.
> - *


Could you say something about QCRYPTO_TLS_SESSION_PREMATURE_TERMINATION
being a possible return code here (no need to repost just for that). 

>   * It is an error to call this before
>   * qcrypto_tls_session_handshake() returns
>   * QCRYPTO_TLS_HANDSHAKE_COMPLETE
> @@ -282,7 +278,6 @@ ssize_t qcrypto_tls_session_write(QCryptoTLSSession *sess,
>  ssize_t qcrypto_tls_session_read(QCryptoTLSSession *sess,
>                                   char *buf,
>                                   size_t len,
> -                                 bool gracefulTermination,
>                                   Error **errp);
>  
>  /**

> +static bool
> +qio_channel_tls_allow_premature_termination(QIOChannelTLS *tioc, int flags)
> +{
> +    if (flags & QIO_CHANNEL_READ_FLAG_RELAXED_EOF) {
> +        return true;
> +    }
> +
> +    if (qatomic_read(&tioc->shutdown) & QIO_CHANNEL_SHUTDOWN_READ) {
> +        return true;
> +    }
> +
> +    return false;
> +}
>  
>  static ssize_t qio_channel_tls_readv(QIOChannel *ioc,
>                                       const struct iovec *iov,
> @@ -364,8 +377,6 @@ static ssize_t qio_channel_tls_readv(QIOChannel *ioc,
>              tioc->session,
>              iov[i].iov_base,
>              iov[i].iov_len,
> -            flags & QIO_CHANNEL_READ_FLAG_RELAXED_EOF ||
> -            qatomic_load_acquire(&tioc->shutdown) & QIO_CHANNEL_SHUTDOWN_READ,
>              errp);


The original code uses qatomic_load_acquire() while the new code
uses qatomic_read() which imposes weaker ordering constraints.

Does this matter ? I'm not familiar enough with atomics to say
which we need here ?

>          if (ret == QCRYPTO_TLS_SESSION_ERR_BLOCK) {
>              if (got) {
> @@ -373,6 +384,12 @@ static ssize_t qio_channel_tls_readv(QIOChannel *ioc,
>              } else {
>                  return QIO_CHANNEL_ERR_BLOCK;
>              }
> +        } else if (ret == QCRYPTO_TLS_SESSION_PREMATURE_TERMINATION) {
> +            if (qio_channel_tls_allow_premature_termination(tioc, flags)) {
> +                ret = 0;
> +            } else {
> +                return -1;
> +            }
>          } else if (ret < 0) {
>              return -1;
>          }
> -- 
> 2.50.1
> 

With regards,
Daniel
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