Re: [PATCH 1/2] fuse: copy request headers via a stack buffer for io-uring

[Darrick J. Wong]

On Mon, Jul 06, 2026 at 02:17:12PM -0700, Joanne Koong wrote:
> On Mon, Jul 6, 2026 at 12:13 PM Xiang Mei <xmei5@xxxxxxx> 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, 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")
> > Reported-by: Weiming Shi <bestswngs@xxxxxxxxx>
> > Assisted-by: Claude:claude-opus-4-8
> > Signed-off-by: Xiang Mei <xmei5@xxxxxxx>
> 
> Reviewed-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> 
> I think the cc stable@xxxxxxxxxxxxxxx tag is missing here. I added
> stable@ to the cc list on this email, but I'm not sure if they require
> the tag being explicitly in the commit message to get it backported.

I used to like it for XFS once upon a time when we did manual reviews
and QA of LTS branches, because it was a headsup for something that I
should actually watch to make sure it actually showed up in stable-rc.

--D