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

[Jens Axboe <axboe@kernel.dk>]

On 5/4/20 7:53 AM, 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
> 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.

Might be simpler to just pass in the __user pointer for the copy,
ala the below. Totally untested...


diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6d52ff98279d..70361f588c5b 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7760,7 +7760,8 @@ 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 int io_uring_create(unsigned entries, struct io_uring_params *p,
+			   struct io_uring_params __user *params)
 {
 	struct user_struct *user = NULL;
 	struct io_ring_ctx *ctx;
@@ -7863,6 +7864,12 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
 	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;
+
+	if (copy_to_user(params, p, sizeof(*p))) {
+		ret = -EFAULT;
+		goto err;
+	}
+
 	trace_io_uring_create(ret, ctx, p->sq_entries, p->cq_entries, p->flags);
 	return ret;
 err:
@@ -7878,7 +7885,6 @@ 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_uring_params p;
-	long ret;
 	int i;
 
 	if (copy_from_user(&p, params, sizeof(p)))
@@ -7893,14 +7899,7 @@ 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;
-
-	if (copy_to_user(params, &p, sizeof(p)))
-		return -EFAULT;
-
-	return ret;
+	return io_uring_create(entries, &p, params);
 }
 
 SYSCALL_DEFINE2(io_uring_setup, u32, entries,

-- 
Jens Axboe