[PATCH 2/2] io_uring/kbuf: fix infinite loop in io_kbuf_inc_commit()

[Qingyue Zhang]

In io_kbuf_inc_commit(), buf points to a user-mapped memory region,
which means buf->len might be changed between importing and committing.
Add a check to avoid infinite loop when sum of buf->len is less than
len.

Co-developed-by: Suoxing Zhang <aftern00n@xxxxxx>
Signed-off-by: Suoxing Zhang <aftern00n@xxxxxx>
Signed-off-by: Qingyue Zhang <chunzhennn@xxxxxx>
---
 io_uring/kbuf.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 81a13338dfab..80ffe6755598 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -34,11 +34,12 @@ struct io_provide_buf {
 
 static bool io_kbuf_inc_commit(struct io_buffer_list *bl, int len)
 {
+	struct io_uring_buf *buf, *buf_start;
+
+	buf_start = buf = io_ring_head_to_buf(bl->buf_ring, bl->head, bl->mask);
 	while (len) {
-		struct io_uring_buf *buf;
 		u32 this_len;
 
-		buf = io_ring_head_to_buf(bl->buf_ring, bl->head, bl->mask);
 		this_len = min_t(u32, len, buf->len);
 		buf->len -= this_len;
 		if (buf->len) {
@@ -47,6 +48,10 @@ static bool io_kbuf_inc_commit(struct io_buffer_list *bl, int len)
 		}
 		bl->head++;
 		len -= this_len;
+
+		buf = io_ring_head_to_buf(bl->buf_ring, bl->head, bl->mask);
+		if (unlikely(buf == buf_start))
+			break;
 	}
 	return true;
 }
-- 
2.48.1