https://bz.apache.org/bugzilla/show_bug.cgi?id=60296
--- Comment #7 from Rafael David Tinoco <[email protected]> --- Max or Eric, Are there any changes in status of this bug ? I can corroborate to what Max said, and proposed, since I'm analysing a dump that was brought to me, exactly in this situation (and also could find another old bug with the same race condition): https://bz.apache.org/bugzilla/show_bug.cgi?id=58483 These are my notes so far: Problem summary: apr_rmm_init acts as a relocatable memory management initialization it is used in: mod_auth_digest and util_ldap_cache >From the dump was brought to my knowledge, in the following sequence: - util_ldap_compare_node_copy() - util_ald_strdup() - apr_rmm_calloc() - find_block_of_size() Had a "cache->rmm_addr" with no lock at "find_block_of_size()" cache->rmm_addr->lock { type = apr_anylock_none } And an invalid "next" offset (out of rmm->base->firstfree). This rmm_addr was initialized with NULL as a locking mechanism: >From apr-utils: apr_rmm_init() if (!lock) { <-- 2nd argument to apr_rmm_init() nulllock.type = apr_anylock_none; <--- found in the dump nulllock.lock.pm = NULL; lock = &nulllock; } >From apache: # mod_auth_digest sts = apr_rmm_init(&client_rmm, NULL, /* no lock, we'll do the locking ourselves */ apr_shm_baseaddr_get(client_shm), shmem_size, ctx); # util_ldap_cache result = apr_rmm_init(&st->cache_rmm, NULL, apr_shm_baseaddr_get(st->cache_shm), size, st->pool); It appears that the ldap module chose to use "rmm" for memory allocation, using the shared memory approach, but without explicitly definiting a lock to it. Without it, its up to the caller to guarantee that there are locks for rmm synchronization (just like mod_auth_digest does, using global mutexes). Because of that, there was a race condition in "find_block_of_size" and a call touching "rmm->base->firstfree", possibly "move_block()", in a multi-threaded apache environment, since there were no lock guarantees inside rmm logic (lock was "apr_anylock_none" and the locking calls don't do anything). In find_block_of_size: apr_rmm_off_t next = rmm->base->firstfree; We have: rmm->base->firstfree Decimal:356400 Hex:0x57030 But "next" turned into: Name : next Decimal:8320808657351632189 Hex:0x737973636970653d Causing: struct rmm_block_t *blk = (rmm_block_t*)((char*)rmm->base + next); if (blk->size == size) To segfault. -- You are receiving this mail because: You are the assignee for the bug. --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
