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

[Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>]

hi,

> 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
Yeah, I'll add more explanation in commit message, thanks.

Regards,
Xiaoguang Wnag
> 
> 
>> 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;
>>   }
>>
>