[SRU][F][PATCH 1/1] io_uring: ensure IOPOLL locks around deferred work

[Juerg Haefliger]

On Fri, 27 Sep 2024 14:37:51 +0800
Chengen Du <chengen.du at canonical.com> wrote:

> From: Jens Axboe <axboe at kernel.dk>
> 
> CVE-2023-21400
> 
> BugLink: https://bugs.launchpad.net/bugs/2078659
> 
> No direct upstream commit exists for this issue. It was fixed in
> 5.18 as part of a larger rework of the completion side.
> 
> io_commit_cqring() writes the CQ ring tail to make it visible, but it
> also kicks off any deferred work we have. A ring setup with IOPOLL
> does not need any locking around the CQ ring updates, as we're always
> under the ctx uring_lock. But if we have deferred work that needs
> processing, then io_queue_deferred() assumes that the completion_lock
> is held, as it is for !IOPOLL.
> 
> Add a lockdep assertion to check and document this fact, and have
> io_iopoll_complete() check if we have deferred work and run that
> separately with the appropriate lock grabbed.
> 
> Cc: stable at vger.kernel.org # 5.10, 5.15
> Reported-by: dghost david <daviduniverse18 at gmail.com>
> Signed-off-by: Jens Axboe <axboe at kernel.dk>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> (backported from commit fb348857e7b67eefe365052f1423427b66dedbf3)
> [chengen - apply the locking logic to the corresponding functions /
> use spin_lock_irq because the same lock is used in the timer callback
> function.]
> Signed-off-by: Chengen Du <chengen.du at canonical.com>
> ---
>  fs/io_uring.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 875dd8e0f766..aa75c32f2d16 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -512,6 +512,8 @@ static void __io_commit_cqring(struct io_ring_ctx *ctx)
>  {
>  	struct io_rings *rings = ctx->rings;
>  
> +	lockdep_assert_held(&ctx->completion_lock);
> +
>  	if (ctx->cached_cq_tail != READ_ONCE(rings->cq.tail)) {
>  		/* order cqe stores with ring update */
>  		smp_store_release(&rings->cq.tail, ctx->cached_cq_tail);
> @@ -841,7 +843,9 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
>  		}
>  	}
>  
> +	spin_lock_irq(&ctx->completion_lock);
>  	io_commit_cqring(ctx);
> +	spin_unlock_irq(&ctx->completion_lock);
>  	io_free_req_many(ctx, reqs, &to_free);
>  }
>  

Not sure if that is sufficient. Your patch is (obviously) vastly different
from the original. You might want to check SUSE fix for 5.3:
https://github.com/SUSE/kernel/commit/a16c5d2daa1cf45f8694ff72bd2665d474a763a7

Do you have a reproducer to actually validate the fix?

...Juerg
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