CVE-2024-50121
Description
From CVE.org
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 ==================================================================== 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.
Mitigation
To mitigate this issue, prevent module nfsd from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.7 | 7.8 | 7.8 |
| Attack Vector | Local | Local | Local |
| Attack Complexity | High | Low | Low |
| Privileges Required | High | Low | Low |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | None | High | High |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Red Hat CVSS v3 Score Explanation
Only privileged users can trigger it (with writing to the /proc/fs/nfsd/threads). The attack complexity and privileges required is high and has been marked as such.
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
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