[PATCH] io_uring: fix possible use after free to sqd

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

Reading codes finds a possible use after free issue to sqd:
          thread1              |       thread2
==> io_attach_sq_data()        |
===> sqd = ctx_attach->sq_data;|
                               | ==> io_put_sq_data()
                               | ===> refcount_dec_and_test(&sqd->refs)
                               |     If sqd->refs is zero, will free sqd.
                               |
===> refcount_inc(&sqd->refs); |
                               |
                               | ====> kfree(sqd);
===> now use after free to sqd |

Use refcount_inc_not_zero() to fix this issue.

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
---
 fs/io_uring.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 33b5cf18bb51..48e230feb704 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6868,7 +6868,11 @@ static struct io_sq_data *io_attach_sq_data(struct io_uring_params *p)
 		return ERR_PTR(-EINVAL);
 	}
 
-	refcount_inc(&sqd->refs);
+	if (!refcount_inc_not_zero(&sqd->refs)) {
+		fdput(f);
+		return ERR_PTR(-EINVAL);
+	}
+
 	fdput(f);
 	return sqd;
 }
-- 
2.17.2