Bug 2422780 (CVE-2025-68262)

Summary: CVE-2025-68262 kernel: crypto: zstd - fix double-free in per-CPU stream cleanup
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2486302, 2486303    
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Description OSIDB Bzimport 2025-12-16 15:04:27 UTC 
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.