CVE-2024-40900

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

cachefiles: remove requests from xarray during flushing requests

Even with CACHEFILES_DEAD set, we can still read the requests, so in the

following concurrency the request may be used after it has been freed:

mount | daemon_thread1 | daemon_thread2

------------------------------------------------------------

cachefiles_ondemand_init_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

// close dev fd

cachefiles_flush_reqs

complete(&REQ_A->done)

kfree(REQ_A)

xa_lock(&cache->reqs);

cachefiles_ondemand_select_req

req->msg.opcode != CACHEFILES_OP_READ

// req use-after-free !!!

xa_unlock(&cache->reqs);

xa_destroy(&cache->reqs)

Hence remove requests from cache->reqs when flushing them to avoid

accessing freed requests.