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---