CVE-2024-50121

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 /* wont wait shrinker exit / / cancel_work(&nn->nfsd_shrinker_work)

• nfsd_file for this /* wont 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

==================================================================== BUG nfsd_file_mark (Tainted: G B W ): Objects remaining nfsd_file_mark on __kmem_cache_shutdown()

dump_stack_lvl+0x53/0x70 slab_err+0xb0/0xf0 __kmem_cache_shutdown+0x15c/0x310 kmem_cache_destroy+0x66/0x160 nfsd_file_cache_shutdown+0xc8/0x210 [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

To resolve this issue, cancel nfsd_shrinker_work using synchronous mode in nfs4_state_shutdown_net.

Weakness

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.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/36775f42e039b01d4abe8998bf66771a37d3cdcc
• https://git.kernel.org/stable/c/5ade4382de16c34d9259cb548f36ec5c4555913c
• https://git.kernel.org/stable/c/add1df5eba163a3a6ece11cb85890e2e410baaea
• https://git.kernel.org/stable/c/d5ff2fb2e7167e9483846e34148e60c0c016a1f6
• https://git.kernel.org/stable/c/f67138dd338cb564ade7d3755c8cd4f68b46d397
• https://git.kernel.org/stable/c/f965dc0f099a54fca100acf6909abe52d0c85328