CVE-2024-56779

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

nfsd: fix nfs4_openowner leak when concurrent nfsd4_open occur

The action force umount(umount -f) will attempt to kill all rpc_task even umount operation may ultimately fail if some files remain open. Consequently, if an action attempts to open a file, it can potentially send two rpc_task to nfs server.

               NFS CLIENT

thread1 thread2 open("file") ... nfs4_do_open _nfs4_do_open _nfs4_open_and_get_state _nfs4_proc_open nfs4_run_open_task /* rpc_task1 */ rpc_run_task rpc_wait_for_completion_task

                                umount -f
                                nfs_umount_begin
                                 rpc_killall_tasks
                                  rpc_signal_task
 rpc_task1 been wakeup
 and return -512

_nfs4_do_open // while loop ... nfs4_run_open_task /* rpc_task2 */ rpc_run_task rpc_wait_for_completion_task

While processing an open request, nfsd will first attempt to find or allocate an nfs4_openowner. If it finds an nfs4_openowner that is not marked as NFS4_OO_CONFIRMED, this nfs4_openowner will released. Since two rpc_task can attempt to open the same file simultaneously from the client to server, and because two instances of nfsd can run concurrently, this situation can lead to lots of memory leak. Additionally, when we echo 0 to /proc/fs/nfsd/threads, warning will be triggered.

                NFS SERVER

nfsd1 nfsd2 echo 0 > /proc/fs/nfsd/threads

nfsd4_open nfsd4_process_open1 find_or_alloc_open_stateowner // alloc oo1, stateid1 nfsd4_open nfsd4_process_open1 find_or_alloc_open_stateowner // find oo1, without NFS4_OO_CONFIRMED release_openowner unhash_openowner_locked list_del_init(&oo->oo_perclient) // cannot find this oo // from client, LEAK!!! alloc_stateowner // alloc oo2

nfsd4_process_open2 init_open_stateid // associate oo1 // with stateid1, stateid1 LEAK!!! nfs4_get_vfs_file // alloc nfsd_file1 and nfsd_file_mark1 // all LEAK!!!

                     nfsd4_process_open2
                     ...

                                write_threads
                                 ...
                                 nfsd_destroy_serv
                                  nfsd_shutdown_net
                                   nfs4_state_shutdown_net
                                    nfs4_state_destroy_net
                                     destroy_client
                                      __destroy_client
                                      // won't find oo1!!!
                                 nfsd_shutdown_generic
                                  nfsd_file_cache_shutdown
                                   kmem_cache_destroy
                                   for nfsd_file_slab
                                   and nfsd_file_mark_slab
                                   // bark since nfsd_file1
                                   // and nfsd_file_mark1
                                   // still alive

======================================================================= BUG nfsd_file (Not tainted): Objects remaining in nfsd_file on __kmem_cache_shutdown()

Slab 0xffd4000004438a80 objects=34 used=1 fp=0xff11000110e2ad28 flags=0x17ffffc0000240(workingset|head|node=0|zone=2|lastcpupid=0x1fffff) CPU: 4 UID: 0 PID: 757 Comm: sh Not tainted 6.12.0-rc6+ #19 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 Call Trace: <TASK> dum ---truncated---

This vulnerability is rated as Moderate severity because it is limited to a denial-of-service condition through kernel memory exhaustion and does not compromise system confidentiality or integrity. On Red Hat Enterprise Linux systems, the kernel NFS server is not active by default; exposure is restricted to systems explicitly configured to export directories to NFSv4 clients. Exploitation depends on concurrent file open requests racing during client state handling, causing unreleased resource allocations within server-side state tracking.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.