CVE-2024-39510 Information

Description

In the Linux kernel the following vulnerability has been resolved:

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

We got the following issue in a fuzz test of randomly issuing the restore command:

================================================================== BUG: KASAN: slab-use-after-free in cachefiles_ondemand_daemon_read+0xb41/0xb60 Read of size 8 at addr ffff888122e84088 by task ondemand-04-dae/963

CPU: 13 PID: 963 Comm: ondemand-04-dae Not tainted 6.8.0-dirty 564 Call Trace: kasan_report+0x93/0xc0 cachefiles_ondemand_daemon_read+0xb41/0xb60 vfs_read+0x169/0xb50 ksys_read+0xf5/0x1e0

Allocated by task 116: kmem_cache_alloc+0x140/0x3a0 cachefiles_lookup_cookie+0x140/0xcd0 fscache_cookie_state_machine+0x43c/0x1230 […]

Freed by task 792: kmem_cache_free+0xfe/0x390 cachefiles_put_object+0x241/0x480 fscache_cookie_state_machine+0x5c8/0x1230 […]

Following is the process that triggers the issue:

 mount  |   daemon_thread1    |    daemon_thread2

cachefiles_withdraw_cookie cachefiles_ondemand_clean_object(object) cachefiles_ondemand_send_req REQ_A = kzalloc(sizeof(req) + data_len) wait_for_completion(&REQ_A->done)

        cachefiles_daemon_read
         cachefiles_ondemand_daemon_read
          REQ_A = cachefiles_ondemand_select_req
          msg->object_id = req->object->ondemand->ondemand_id
                              ------ restore ------
                              cachefiles_ondemand_restore
                              xas_for_each(&xas req ULONG_MAX)
                               xas_set_mark(&xas CACHEFILES_REQ_NEW)

                              cachefiles_daemon_read
                               cachefiles_ondemand_daemon_read
                                REQ_A = cachefiles_ondemand_select_req
          copy_to_user(_buffer msg n)
           xa_erase(&cache->reqs id)
           complete(&REQ_A->done)
          ------ close(fd) ------
          cachefiles_ondemand_fd_release
           cachefiles_put_object

cachefiles_put_object kmem_cache_free(cachefiles_object_jar object) REQ_A->object->ondemand->ondemand_id // object UAF !!!

When we see the request within xa_lock req->object must not have been freed yet so grab the reference count of object before xa_unlock to avoid the above issue.

Reference

https://git.kernel.org/stable/c/cb55625f8eb9d2de8be4da0c4580d48cbb32058e https://git.kernel.org/stable/c/3958679c49152391209b32be3357193300a51abd https://git.kernel.org/stable/c/93064676a2820420a2d37d7c8289f277fe20793d https://git.kernel.org/stable/c/da4a827416066191aafeeccee50a8836a826ba10