CVE-2024-56558

/// Technical description

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

nfsd: make sure exp active before svc_export_show

The function `e_show` was called with protection from RCU. This only

ensures that `exp` will not be freed. Therefore, the reference count for

`exp` can drop to zero, which will trigger a refcount use-after-free

warning when `exp_get` is called. To resolve this issue, use

`cache_get_rcu` to ensure that `exp` remains active.

------------[ cut here ]------------

refcount_t: addition on 0; use-after-free.

WARNING: CPU: 3 PID: 819 at lib/refcount.c:25

refcount_warn_saturate+0xb1/0x120

CPU: 3 UID: 0 PID: 819 Comm: cat Not tainted 6.12.0-rc3+ #1

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS

1.16.1-2.fc37 04/01/2014

RIP: 0010:refcount_warn_saturate+0xb1/0x120

...

Call Trace:

<TASK>

e_show+0x20b/0x230 [nfsd]

seq_read_iter+0x589/0x770

seq_read+0x1e5/0x270

vfs_read+0x125/0x530

ksys_read+0xc1/0x160

do_syscall_64+0x5f/0x170

entry_SYSCALL_64_after_hwframe+0x7

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References