CVE-2025-68262

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

crypto: zstd - fix double-free in per-CPU stream cleanup

The crypto/zstd module has a double-free bug that occurs when multiple tfms are allocated and freed.

The issue happens because zstd_streams (per-CPU contexts) are freed in zstd_exit() during every tfm destruction, rather than being managed at the module level. When multiple tfms exist, each tfm exit attempts to free the same shared per-CPU streams, resulting in a double-free.

This leads to a stack trace similar to:

BUG: Bad page state in process kworker/u16:1 pfn:106fd93 page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x106fd93 flags: 0x17ffffc0000000(node=0|zone=2|lastcpupid=0x1fffff) page_type: 0xffffffff() raw: 0017ffffc0000000 dead000000000100 dead000000000122 0000000000000000 raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: nonzero entire_mapcount Modules linked in: ... CPU: 3 UID: 0 PID: 2506 Comm: kworker/u16:1 Kdump: loaded Tainted: G B Hardware name: ... Workqueue: btrfs-delalloc btrfs_work_helper Call Trace: <TASK> dump_stack_lvl+0x5d/0x80 bad_page+0x71/0xd0 free_unref_page_prepare+0x24e/0x490 free_unref_page+0x60/0x170 crypto_acomp_free_streams+0x5d/0xc0 crypto_acomp_exit_tfm+0x23/0x50 crypto_destroy_tfm+0x60/0xc0 ...

Change the lifecycle management of zstd_streams to free the streams only once during module cleanup.

This vulnerability is rated as Moderate impact because triggering the flaw requires local execution privileges to create and release multiple cryptographic transform instances, limiting the risk primarily to a localized kernel denial of service. Under typical Red Hat Enterprise Linux deployments, the issue arises when kernel services or local consumers tear down multiple Zstandard compression handles through the kernel crypto API, leading to improper memory reuse and kernel panic. Remote attackers cannot reach this code path directly, and the defect does not grant privilege escalation or data confidentiality exposure on supported systems.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.