commit 1b551823de6e6c03cf86bcbb7ca1b687c5f16ea6 Author: Nick Mathewson nickm@torproject.org Date: Tue Jun 10 11:11:47 2014 -0400
Avoid illegal read off end of an array in prune_v2_cipher_list
This function is supposed to construct a list of all the ciphers in the "v2 link protocol cipher list" that are supported by Tor's openssl. It does this by invoking ssl23_get_cipher_by_char on each two-byte ciphersuite ID to see which ones give a match. But when ssl23_get_cipher_by_char cannot find a match for a two-byte SSL3/TLS ciphersuite ID, it checks to see whether it has a match for a three-byte SSL2 ciphersuite ID. This was causing a read off the end of the 'cipherid' array.
This was probably harmless in practice, but we shouldn't be having any uninitialized reads.
(Using ssl23_get_cipher_by_char in this way is a kludge, but then again the entire existence of the v2 link protocol is kind of a kludge. Once Tor 0.2.2 clients are all gone, we can drop this code entirely.)
Found by starlight. Fix on 0.2.4.8-alpha. Fixes bug 12227. --- changes/bug12227 | 5 +++++ src/common/tortls.c | 5 ++++- 2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/changes/bug12227 b/changes/bug12227 new file mode 100644 index 0000000..d8b5d08 --- /dev/null +++ b/changes/bug12227 @@ -0,0 +1,5 @@ + o Minor bugfixes: + - Avoid an illegal read from stack when initializing the TLS + module using a version of OpenSSL without all of the ciphers + used by the v2 link handshake. Fixes bug 12227; bugfix on + 0.2.4.8-alpha. Found by "starlight". diff --git a/src/common/tortls.c b/src/common/tortls.c index 8f3f6a7..c13b12f 100644 --- a/src/common/tortls.c +++ b/src/common/tortls.c @@ -1489,10 +1489,13 @@ prune_v2_cipher_list(void)
inp = outp = v2_cipher_list; while (*inp) { - unsigned char cipherid[2]; + unsigned char cipherid[3]; const SSL_CIPHER *cipher; /* Is there no better way to do this? */ set_uint16(cipherid, htons(*inp)); + cipherid[2] = 0; /* If ssl23_get_cipher_by_char finds no cipher starting + * with a two-byte 'cipherid', it may look for a v2 + * cipher with the appropriate 3 bytes. */ cipher = m->get_cipher_by_char(cipherid); if (cipher) { tor_assert((cipher->id & 0xffff) == *inp);