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

Summary

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.

Timeline

1. Sep 11, 2026, 7:42 PM UTCCVE published
2. Oct 19, 2026, 8:45 AM UTCRecord last updated

Affected versions

• Linux Linux

  From c090c8abae4b6b77a1bee116aa6c385456ebef96 · fixed in 194d0fb0ea4720535ff3168c9d04c7632cec7071; From c090c8abae4b6b77a1bee116aa6c385456ebef96 · fixed in a47a416ff68d706dc3327ab583f86b9ee757358b; From c090c8abae4b6b77a1bee116aa6c385456ebef96 · fixed in fd10f40af314f07b6d6e028b1ca25c8b49903aab

• Linux Linux

  6.14

• KernelLinux

  From 6.14.0 · fixed in 6.18.51; From 6.19.0 · fixed in 7.2.4

References 3