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

[Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxx>
> > ---
> >   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;
> >   }