7

CVE-2024-41057

In the Linux kernel, the following vulnerability has been resolved:

cachefiles: fix slab-use-after-free in cachefiles_withdraw_cookie()

We got the following issue in our fault injection stress test:

==================================================================
BUG: KASAN: slab-use-after-free in cachefiles_withdraw_cookie+0x4d9/0x600
Read of size 8 at addr ffff888118efc000 by task kworker/u78:0/109

CPU: 13 PID: 109 Comm: kworker/u78:0 Not tainted 6.8.0-dirty #566
Call Trace:
 <TASK>
 kasan_report+0x93/0xc0
 cachefiles_withdraw_cookie+0x4d9/0x600
 fscache_cookie_state_machine+0x5c8/0x1230
 fscache_cookie_worker+0x91/0x1c0
 process_one_work+0x7fa/0x1800
 [...]

Allocated by task 117:
 kmalloc_trace+0x1b3/0x3c0
 cachefiles_acquire_volume+0xf3/0x9c0
 fscache_create_volume_work+0x97/0x150
 process_one_work+0x7fa/0x1800
 [...]

Freed by task 120301:
 kfree+0xf1/0x2c0
 cachefiles_withdraw_cache+0x3fa/0x920
 cachefiles_put_unbind_pincount+0x1f6/0x250
 cachefiles_daemon_release+0x13b/0x290
 __fput+0x204/0xa00
 task_work_run+0x139/0x230
 do_exit+0x87a/0x29b0
 [...]
==================================================================

Following is the process that triggers the issue:

           p1                |             p2
------------------------------------------------------------
                              fscache_begin_lookup
                               fscache_begin_volume_access
                                fscache_cache_is_live(fscache_cache)
cachefiles_daemon_release
 cachefiles_put_unbind_pincount
  cachefiles_daemon_unbind
   cachefiles_withdraw_cache
    fscache_withdraw_cache
     fscache_set_cache_state(cache, FSCACHE_CACHE_IS_WITHDRAWN);
    cachefiles_withdraw_objects(cache)
    fscache_wait_for_objects(fscache)
      atomic_read(&fscache_cache->object_count) == 0
                              fscache_perform_lookup
                               cachefiles_lookup_cookie
                                cachefiles_alloc_object
                                 refcount_set(&object->ref, 1);
                                 object->volume = volume
                                 fscache_count_object(vcookie->cache);
                                  atomic_inc(&fscache_cache->object_count)
    cachefiles_withdraw_volumes
     cachefiles_withdraw_volume
      fscache_withdraw_volume
      __cachefiles_free_volume
       kfree(cachefiles_volume)
                              fscache_cookie_state_machine
                               cachefiles_withdraw_cookie
                                cache = object->volume->cache;
                                // cachefiles_volume UAF !!!

After setting FSCACHE_CACHE_IS_WITHDRAWN, wait for all the cookie lookups
to complete first, and then wait for fscache_cache->object_count == 0 to
avoid the cookie exiting after the volume has been freed and triggering
the above issue. Therefore call fscache_withdraw_volume() before calling
cachefiles_withdraw_objects().

This way, after setting FSCACHE_CACHE_IS_WITHDRAWN, only the following two
cases will occur:
1) fscache_begin_lookup fails in fscache_begin_volume_access().
2) fscache_withdraw_volume() will ensure that fscache_count_object() has
   been executed before calling fscache_wait_for_objects().
Daten sind bereitgestellt durch National Vulnerability Database (NVD)
Linux ≫ Linux Kernel Version >= 5.17 < 6.1.101
Linux ≫ Linux Kernel Version >= 6.2 < 6.6.42
Linux ≫ Linux Kernel Version >= 6.7 < 6.9.11
Zu dieser CVE wurde keine CISA KEV oder CERT.AT-Warnung gefunden.
EPSS Metriken
Typ Quelle Score Percentile
EPSS FIRST.org 0.01% 0.016
CVSS Metriken
Quelle Base Score Exploit Score Impact Score Vector String
nvd@nist.gov 7 1 5.9
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE-416 Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.