Re: [PATCH] io_uring: fix missing submitter_task ownership check in bpf_io_reg()

[Pavel Begunkov <asml.silence@gmail.com>]

On 4/22/26 22:20, Gabriel Krisman Bertazi wrote:
> Ali Raza <elirazamumtaz@gmail.com> writes:
> 
>> bpf_io_reg() installs a BPF struct_ops loop_step on any io_uring ring
>> the caller holds a file descriptor for.  io_uring_ctx_get_file() only
>> validates that the fd resolves to an io_uring file; it does not verify
>> the caller has authority over the ring's submitter_task.
>>
>> A parallel path in io_uring_register() already enforces this:
>>
>>      if (ctx->submitter_task && ctx->submitter_task != current)
>>          return -EEXIST;  /* register.c:733 */
> 
> How is this a protection?  I thought ctx->submitter_task is about
> IORING_SETUP_SINGLE_ISSUER. there is no permission or capability over
> it against other processes.
> 
>> Without the equivalent check in bpf_io_reg(), a local user with
>> CAP_PERFMON can exploit IORING_SETUP_R_DISABLED -- which defers
> 
> I'd argue this is a non-issue.

Right, it involves receiving a ring from an untrusted source and
then using it. Any application doing that is extremely broken,
even without any bpf you can use that to do some pretty nasty things

   If you have CAP_PERFMON, you are able to
> mess with the process in many ways beyond this.  Otherwise, how a
> process would be able to get the fd in the first place?



-- 
Pavel Begunkov