Re: [PATCH] io_uring: handle -EFAULT properly in io_uring_setup()

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

On 04/05/2020 16:53, Xiaoguang Wang wrote:
> If copy_to_user() in io_uring_setup() failed, we'll leak many kernel
> resources, which could be reproduced by using mprotect to set params

At least it recycles everything upon killing the process, so that's rather not
notifying a user about a successfully installed fd. Good catch


> to PROT_READ. To fix this issue, refactor io_uring_create() a bit to
> let it return 'struct io_ring_ctx *', then when copy_to_user() failed,
> we can free kernel resource properly.
> 
> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
> ---
>  fs/io_uring.c | 45 ++++++++++++++++++++++++---------------------
>  1 file changed, 24 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 0b91b0631173..a19885dee621 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -7761,7 +7761,8 @@ static int io_uring_get_fd(struct io_ring_ctx *ctx)
>  	return ret;
>  }
>  
> -static int io_uring_create(unsigned entries, struct io_uring_params *p)
> +static struct io_ring_ctx *io_uring_create(unsigned entries,
> +				struct io_uring_params *p)
>  {
>  	struct user_struct *user = NULL;
>  	struct io_ring_ctx *ctx;
> @@ -7769,10 +7770,10 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
>  	int ret;
>  
>  	if (!entries)
> -		return -EINVAL;
> +		return ERR_PTR(-EINVAL);
>  	if (entries > IORING_MAX_ENTRIES) {
>  		if (!(p->flags & IORING_SETUP_CLAMP))
> -			return -EINVAL;
> +			return ERR_PTR(-EINVAL);
>  		entries = IORING_MAX_ENTRIES;
>  	}
>  
> @@ -7792,10 +7793,10 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
>  		 * any cq vs sq ring sizing.
>  		 */
>  		if (p->cq_entries < p->sq_entries)
> -			return -EINVAL;
> +			return ERR_PTR(-EINVAL);
>  		if (p->cq_entries > IORING_MAX_CQ_ENTRIES) {
>  			if (!(p->flags & IORING_SETUP_CLAMP))
> -				return -EINVAL;
> +				return ERR_PTR(-EINVAL);
>  			p->cq_entries = IORING_MAX_CQ_ENTRIES;
>  		}
>  		p->cq_entries = roundup_pow_of_two(p->cq_entries);
> @@ -7811,7 +7812,7 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
>  				ring_pages(p->sq_entries, p->cq_entries));
>  		if (ret) {
>  			free_uid(user);
> -			return ret;
> +			return ERR_PTR(ret);
>  		}
>  	}
>  
> @@ -7821,7 +7822,7 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
>  			io_unaccount_mem(user, ring_pages(p->sq_entries,
>  								p->cq_entries));
>  		free_uid(user);
> -		return -ENOMEM;
> +		return ERR_PTR(-ENOMEM);
>  	}
>  	ctx->compat = in_compat_syscall();
>  	ctx->account_mem = account_mem;
> @@ -7853,22 +7854,14 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
>  	p->cq_off.overflow = offsetof(struct io_rings, cq_overflow);
>  	p->cq_off.cqes = offsetof(struct io_rings, cqes);
>  
> -	/*
> -	 * Install ring fd as the very last thing, so we don't risk someone
> -	 * having closed it before we finish setup
> -	 */
> -	ret = io_uring_get_fd(ctx);
> -	if (ret < 0)
> -		goto err;
> -
>  	p->features = IORING_FEAT_SINGLE_MMAP | IORING_FEAT_NODROP |
>  			IORING_FEAT_SUBMIT_STABLE | IORING_FEAT_RW_CUR_POS |
>  			IORING_FEAT_CUR_PERSONALITY | IORING_FEAT_FAST_POLL;
>  	trace_io_uring_create(ret, ctx, p->sq_entries, p->cq_entries, p->flags);
> -	return ret;
> +	return ctx;
>  err:
>  	io_ring_ctx_wait_and_kill(ctx);
> -	return ret;
> +	return ERR_PTR(ret);
>  }
>  
>  /*
> @@ -7878,6 +7871,7 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
>   */
>  static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
>  {
> +	struct io_ring_ctx *ctx;
>  	struct io_uring_params p;
>  	long ret;
>  	int i;
> @@ -7894,12 +7888,21 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
>  			IORING_SETUP_CLAMP | IORING_SETUP_ATTACH_WQ))
>  		return -EINVAL;
>  
> -	ret = io_uring_create(entries, &p);
> -	if (ret < 0)
> -		return ret;
> +	ctx = io_uring_create(entries, &p);
> +	if (IS_ERR(ctx))
> +		return PTR_ERR(ctx);
>  
> -	if (copy_to_user(params, &p, sizeof(p)))
> +	if (copy_to_user(params, &p, sizeof(p))) {
> +		io_ring_ctx_wait_and_kill(ctx);
>  		return -EFAULT;
> +	}
> +	/*
> +	 * Install ring fd as the very last thing, so we don't risk someone
> +	 * having closed it before we finish setup
> +	 */
> +	ret = io_uring_get_fd(ctx);
> +	if (ret < 0)
> +		io_ring_ctx_wait_and_kill(ctx);
>  
>  	return ret;
>  }
> 

-- 
Pavel Begunkov