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[Rafael David Tinoco <rafael.tinoco@xxxxxxxxxxxxx>]

Public bug reported:


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.

Upstream bugs:

https://bz.apache.org/bugzilla/show_bug.cgi?id=58483
https://bz.apache.org/bugzilla/show_bug.cgi?id=60296
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=814980#15

** Affects: apache2 (Ubuntu)
     Importance: Medium
     Assignee: Rafael David Tinoco (inaddy)
         Status: In Progress


** Tags: sts

** Changed in: apache2 (Ubuntu)
       Status: New => In Progress

** Changed in: apache2 (Ubuntu)
     Assignee: (unassigned) => Rafael David Tinoco (inaddy)

** Changed in: apache2 (Ubuntu)
   Importance: Undecided => Medium

** Tags added: sts

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https://bugs.launchpad.net/bugs/1752683

Title:
  race condition on rmm for module ldap (ldap cache)

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