TLDRVuln - Cybersecurity Vulnerabilities Made Simple

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

nfsd: cancel nfsd_shrinker_work using sync mode in nfs4_state_shutdown_net

In the normal case, when we excute `echo 0 > /proc/fs/nfsd/threads`, the

function `nfs4_state_destroy_net` in `nfs4_state_shutdown_net` will

release all resources related to the hashed `nfs4_client`. If the

`nfsd_client_shrinker` is running concurrently, the `expire_client`

function will first unhash this client and then destroy it. This can

lead to the following warning. Additionally, numerous use-after-free

errors may occur as well.

nfsd_client_shrinker echo 0 > /proc/fs/nfsd/threads

expire_client nfsd_shutdown_net

unhash_client ...

nfs4_state_shutdown_net

/* won't wait shrinker exit */

/* cancel_work(&nn->nfsd_shrinker_work)

* nfsd_file for this /* won't destroy unhashed client1 */

* client1 still alive nfs4_state_destroy_net

nfsd_file_cache_shutdown

/* trigger warning */

kmem_cache_destroy(nfsd_file_slab)

kmem_cache_destroy(nfsd_file_mark_slab)

/* release nfsd_file and mark */

__destroy_client

====================================================================

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

__kmem_cache_shutdown()

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

CPU: 4 UID: 0 PID: 764 Comm: sh Not tainted 6.12.0-rc3+ #1

dump_stack_lvl+0x53/0x70

slab_err+0xb0/0xf0

__kmem_cache_shutdown+0x15c/0x310

kmem_cache_destroy+0x66/0x160

nfsd_file_cache_shutdown+0xac/0x210 [nfsd]

nfsd_destroy_serv+0x251/0x2a0 [nfsd]

nfsd_svc+0x125/0x1e0 [nfsd]

write_threads+0x16a/0x2a0 [nfsd]

nfsctl_transaction_write+0x74/0xa0 [nfsd]

vfs_write+0x1a5/0x6d0

ksys_write+0xc1/0x160

do_syscall_64+0x5f/0x170

entry_SYSCALL_64_after_hwframe+0x76/0x7e