Re: [PATCH] io_uring: cast id to u64 before shifting in io_allocate_rbuf_ring()

On 3/16/26 9:06 AM, Anas Iqbal wrote:

Smatch warns:
io_uring/zcrx.c:393 io_allocate_rbuf_ring() warn: should 'id << 16' be a 64 bit type?

The expression 'id << IORING_OFF_PBUF_SHIFT' is evaluated using 32-bit
arithmetic because id is a u32. This may overflow before being promoted
to the 64-bit mmap_offset.

Cast id to u64 before shifting to ensure the shift is performed in
64-bit arithmetic.

I'd be impressed if 'id' could be large enough to cause this to
overflow. AFAICT, you'd need more than 64K interface queues registered
to hit this. So I think this should be reframed as a cleanup, to appease
smatch.

I'll defer to Pavel on that one.

-- 
Jens Axboe