Hi Xiang,
On 2026/7/10 05:11, Xiang Mei wrote:
> 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,
Then why not allocate "fuse_request" with kmem_cache_create_usercopy()
to add a usercopy whitelist instead?
That would avoid the extra stack usage for the bounce headers and
the 56 bytes of copying they incur.
Thanks,
Baokun
> 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!
> RIP: 0010:usercopy_abort+0x6c/0x80
> Call Trace:
> __check_heap_object
> __check_object_size
> copy_header_to_ring fs/fuse/dev_uring.c:618
> fuse_uring_prepare_send
> fuse_uring_send_in_task
> ...
> __do_sys_io_uring_enter
> entry_SYSCALL_64_after_hwframe
>
> 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: [email protected]
> Reported-by: Weiming Shi <[email protected]>
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Xiang Mei <[email protected]>
> Reviewed-by: Bernd Schubert <[email protected]>
> Reviewed-by: Joanne Koong <[email protected]>
> ---
> v3: no context change; add Bernd's Reviewed-by
>
> 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 77c8cec43d9c..0814681eb04b 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -744,6 +744,7 @@ static int fuse_uring_copy_to_ring(struct fuse_ring_ent
> *ent,
> {
> struct fuse_ring_queue *queue = ent->queue;
> struct fuse_ring *ring = queue->ring;
> + struct fuse_in_header in_header;
> int err;
>
> err = -EIO;
> @@ -765,8 +766,9 @@ 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 int fuse_uring_prepare_send(struct fuse_ring_ent *ent,
> @@ -871,11 +873,13 @@ static void fuse_uring_commit(struct fuse_ring_ent
> *ent, struct fuse_req *req,
> unsigned int issue_flags)
> {
> struct fuse_ring *ring = ent->queue->ring;
> + 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) {
