From fd10f40af314f07b6d6e028b1ca25c8b49903aab Mon Sep 17 00:00:00 2001 From: Xiang Mei Date: Mon, 27 Jul 2026 16:37:04 -0700 Subject: [PATCH] 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. Fixes: c090c8abae4b ("fuse: Add io-uring sqe commit and fetch support") Cc: stable@vger.kernel.org Reported-by: Weiming Shi Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Xiang Mei Reviewed-by: Bernd Schubert Reviewed-by: Joanne Koong Signed-off-by: Miklos Szeredi --- fs/fuse/dev_uring.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c index 1547a4f0d9b9..e22a48c9a678 100644 --- a/fs/fuse/dev_uring.c +++ b/fs/fuse/dev_uring.c @@ -922,6 +922,7 @@ static int fuse_uring_copy_to_ring(struct fuse_ring_ent *ent, unsigned int issue_flags) { struct fuse_ring_queue *queue = ent->queue; + struct fuse_in_header in_header; int err; err = -EIO; @@ -943,8 +944,9 @@ static int fuse_uring_copy_to_ring(struct fuse_ring_ent *ent, } /* copy fuse_in_header */ - return copy_header_to_ring(ent, FUSE_URING_HEADER_IN_OUT, &req->in.h, - sizeof(req->in.h)); + in_header = req->in.h; + return copy_header_to_ring(ent, FUSE_URING_HEADER_IN_OUT, &in_header, + sizeof(in_header)); } static bool fuse_uring_req_has_copyable_payload(struct fuse_ring_ent *ent, @@ -1151,11 +1153,13 @@ static struct fuse_req *fuse_uring_ent_assign_req(struct fuse_ring_ent *ent) static void fuse_uring_commit(struct fuse_ring_ent *ent, struct fuse_req *req, unsigned int issue_flags) { + struct fuse_out_header out_header; ssize_t err = -EFAULT; - if (copy_header_from_ring(ent, FUSE_URING_HEADER_IN_OUT, &req->out.h, - sizeof(req->out.h))) + if (copy_header_from_ring(ent, FUSE_URING_HEADER_IN_OUT, &out_header, + sizeof(out_header))) goto out; + req->out.h = out_header; err = fuse_uring_out_header_has_err(&req->out.h, req); if (err) {