Commit bd5d27c1 authored by David Benjamin's avatar David Benjamin Committed by Rich Salz
Browse files

Don't read uninitialised data for short session IDs. 

While it's always safe to read |SSL_MAX_SSL_SESSION_ID_LENGTH| bytes
from an |SSL_SESSION|'s |session_id| array, the hash function would do
so with without considering if all those bytes had been written to.

This change checks |session_id_length| before possibly reading
uninitialised memory. Since the result of the hash function was already
attacker controlled, and since a lookup of a short session ID will
always fail, it doesn't appear that this is anything more than a clean
up.

In particular, |ssl_get_prev_session| uses a stack-allocated placeholder
|SSL_SESSION| as a lookup key, so the |session_id| array may be
uninitialised.

This was originally found with libFuzzer and MSan in
https://boringssl.googlesource.com/boringssl/+/e976e4349d693b4bbb97e1694f45be5a1b22c8c7

,
then by Robert Swiecki with honggfuzz and MSan here. Thanks to both.

Reviewed-by: default avatarGeoff Thorpe <geoff@openssl.org>
Reviewed-by: default avatarRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2583)
parent 76e624a0

ssl/ssl_lib.c

+12 −4
Original line number Diff line number Diff line
@@ -2391,13 +2391,21 @@ int SSL_export_keying_material(SSL *s, unsigned char *out, size_t olen, 


static unsigned long ssl_session_hash(const SSL_SESSION *a)

{

    const unsigned char *session_id = a->session_id;

    unsigned long l;

    unsigned char tmp_storage[4];



    if (a->session_id_length < sizeof(tmp_storage)) {

        memset(tmp_storage, 0, sizeof(tmp_storage));

        memcpy(tmp_storage, a->session_id, a->session_id_length);

        session_id = tmp_storage;

    }



    l = (unsigned long)

        ((unsigned int)a->session_id[0]) |

        ((unsigned int)a->session_id[1] << 8L) |

        ((unsigned long)a->session_id[2] << 16L) |

        ((unsigned long)a->session_id[3] << 24L);

        ((unsigned long)session_id[0]) |

        ((unsigned long)session_id[1] << 8L) |

        ((unsigned long)session_id[2] << 16L) |

        ((unsigned long)session_id[3] << 24L);

    return (l);

}