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由 Benjamin Kaduk 提交于
As was done for ciphers, supported groups, and EC point formats in https://github.com/openssl/openssl/pull/9162, only write the negotiated SNI hostname value to the session object when not resuming, even for TLS 1.3 resumptions. Otherwise, when using a stateful session cache (as is done by default when 0-RTT data is enabled), we can have multiple SSLs active using the same in-memory session object, which leads to double-frees and similar race conditions in the SNI handler prior to this commit. Fortunately, since draft-ietf-tls-tls13-22, there is no requirement that the SNI hostname be preserved across TLS 1.3 resumption, and thus not a need to continually update the session object with the "current" value (to be used when producing session tickets, so that the subsequent resumption can be checked against the current value). So we can just relax the logic and only write to the session object for initial handshakes. This still leaves us in a somewhat inconsistent state, since if the SNI value does change across handshakes, the session object will continue to record the initial handshake's value, even if that bears no relation to the current handshake. The current SSL_get_servername() implementation prefers the value from the session if s->hit, but a more complete fix for that and related issues is underway in https://github.com/openssl/openssl/pull/10018; there is no need to wait for the complete fix for SNI name handling in order to close the race condition and avoid runtime crashes. Reviewed-by: NMatt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/10441)
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