Bug 2532123 (CVE-2026-80946)

Summary: CVE-2026-80946 kernel: fuse: copy request headers via a stack buffer for io-uring
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's FUSE (Filesystem in Userspace) component. The `io-uring` transport attempts to copy request headers directly to or from user space without proper memory validation. A local attacker could exploit this vulnerability, leading to a kernel panic and a denial of service. This issue could also potentially result in the exposure of sensitive kernel memory.
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Description OSIDB Bzimport 2026-09-11 20:46:23 UTC 
In the Linux kernel, the following vulnerability has been resolved:

fuse: copy request headers via a stack buffer for io-uring

The fuse-io-uring transport copies req->in.h out to the ring in
fuse_uring_copy_to_ring() and req->out.h back in fuse_uring_commit().
Both headers live inside the fuse_request slab object, whose cache
(fuse_req_cachep) is created without a usercopy whitelist, so copying
them directly to/from userspace trips CONFIG_HARDENED_USERCOPY and
panics:

  usercopy: Kernel memory exposure attempt detected from SLUB object
  'fuse_request' (offset 56, size 40)!
  kernel BUG at mm/usercopy.c:102!
  Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
  RIP: 0010:usercopy_abort (mm/usercopy.c:90)
  Call Trace:
   __check_heap_object (mm/slub.c:8268)
   __check_object_size (mm/usercopy.c:197 mm/usercopy.c:258 mm/usercopy.c:223)
   copy_header_to_ring (fs/fuse/dev_uring.c:618)
   fuse_uring_prepare_send (fs/fuse/dev_uring.c:776 fs/fuse/dev_uring.c:785)
   fuse_uring_send_in_task (fs/fuse/dev_uring.c:1306)
   tctx_task_work_run (io_uring/tw.c:96)
   task_work_run (kernel/task_work.c:233)
   io_run_task_work (io_uring/tw.h:84)
   io_cqring_wait (io_uring/wait.c:278)
   __do_sys_io_uring_enter (io_uring/io_uring.c:2685)
   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)

Bounce both headers through an on-stack copy so the usercopy touches
stack memory, not the slab object.
Comment 1 Keith Grant 2026-09-14 15:34:06 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-80946.mbox