diff options
| -rw-r--r-- | ychat/src/chat/sman.cpp | 93 |
1 files changed, 71 insertions, 22 deletions
diff --git a/ychat/src/chat/sman.cpp b/ychat/src/chat/sman.cpp index 8026497..ed7a585 100644 --- a/ychat/src/chat/sman.cpp +++ b/ychat/src/chat/sman.cpp @@ -31,6 +31,49 @@ #include "../maps/mtools.h" #include "../contrib/crypt/md5.h" +#include <fstream> +#include <unistd.h> +#include <ctime> + +// Build one candidate session ID of i_len chars drawn from s_valid, using a +// strong random source (/dev/urandom) with a one-time rand() fallback. +// NOTE: deliberately does NOT re-seed srand() with time(0) on every call — +// the old code did that, which (a) made IDs predictable and (b) made two +// logins in the same second produce identical IDs; the collision retry then +// re-seeded with the same time and recursed forever -> stack overflow. +static string +gen_session_candidate( int i_len, const string &s_valid ) +{ + static ifstream urandom( "/dev/urandom", ios::binary ); + static bool b_seeded = false; + + size_t n = s_valid.length(); + string s; + s.reserve( i_len ); + + for ( int i = 0; i < i_len; i++ ) + { + unsigned char b; + if ( urandom.is_open() && urandom.read( (char*)&b, 1 ) ) + s += s_valid[ b % n ]; + else + { + // A failed read sets failbit and would stick forever; clear it so a + // transient failure can self-heal on the next byte (if urandom is + // genuinely unavailable we keep falling back to rand()). + urandom.clear(); + if ( ! b_seeded ) + { + srand( (unsigned) time(0) ^ ( (unsigned) getpid() << 8 ) ); + b_seeded = true; + } + s += s_valid[ rand() % n ]; + } + } + + return s; +} + sman::sman() { i_continous_session_count = i_session_count = 0; @@ -45,35 +88,41 @@ sman::~sman() string sman::generate_id( int i_len ) { string s_valid = wrap::CONF->get_elem("chat.session.validchars"); - string s_ret = ""; - - srand(time(0)+tool::string2int(wrap::CONF->get_elem("chat.session.kloakkey"))); - int i_char; - - - for (int i = 0; i < i_len; i++) + if ( s_valid.empty() || i_len <= 0 ) + return ""; // misconfigured: nothing to build an ID from + + // Bounded collision retry. With /dev/urandom the collision probability is + // negligible, but a bound prevents any pathological case from recursing + // forever (the old code recursed unboundedly and crashed on same-second + // collisions). + for ( int i_try = 0; i_try < 8; i_try++ ) { - i_char = rand() % s_valid.length(); - s_ret += s_valid[i_char]; - } + string s_ret = gen_session_candidate( i_len, s_valid ); - if ( wrap::CONF->get_elem("chat.session.md5hash") == "true" ) - { - string s_salt = wrap::CONF->get_elem("chat.session.md5salt"); - string s_hash(md5::MD5Crypt(s_ret.c_str(), s_salt.c_str())); - s_ret.append(s_hash.substr(s_ret.find(s_salt) + s_salt.length() + 3)); - } + if ( wrap::CONF->get_elem("chat.session.md5hash") == "true" ) + { + string s_salt = wrap::CONF->get_elem("chat.session.md5salt"); + string s_hash(md5::MD5Crypt(s_ret.c_str(), s_salt.c_str())); + s_ret.append(s_hash.substr(s_ret.find(s_salt) + s_salt.length() + 3)); + } - // Prove, if the TempID already exists - sess* p_sess = get_elem(s_ret); + // Prove, if the TempID already exists + if ( ! get_elem(s_ret) ) + return s_ret; - if (p_sess) - { wrap::system_message(SESSEXI); - return generate_id(i_len); } - return s_ret; + // Astronomically unlikely with a strong random source. Return a final + // candidate only if it does NOT collide (so we never overwrite/leak an + // existing session); otherwise bail with an empty ID (login degrades + // gracefully instead of crashing or leaking). + string s_last = gen_session_candidate( i_len, s_valid ); + if ( ! get_elem(s_last) ) + return s_last; + + wrap::system_message("SMAN: gave up finding a unique session id"); + return ""; } sess *sman::create_session( ) |