[PATCH] net/rds: Fix a use after free in rds_message_map_pages

[Lv Yunlong]

In rds_message_map_pages, rds_message_put() will free rm.
Maybe store the value of rm->data.op_sg ahead of rds_message_put()
is better. Otherwise other threads could allocate the freed chunk
and may change the value of rm->data.op_sg.

Signed-off-by: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>
---
 net/rds/message.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/rds/message.c b/net/rds/message.c
index 071a261fdaab..392e3a2f41a0 100644
--- a/net/rds/message.c
+++ b/net/rds/message.c
@@ -347,8 +347,9 @@ struct rds_message *rds_message_map_pages(unsigned long *page_addrs, unsigned in
 	rm->data.op_nents = DIV_ROUND_UP(total_len, PAGE_SIZE);
 	rm->data.op_sg = rds_message_alloc_sgs(rm, num_sgs);
 	if (IS_ERR(rm->data.op_sg)) {
+		struct scatterlist *tmp = rm->data.op_sg;
 		rds_message_put(rm);
-		return ERR_CAST(rm->data.op_sg);
+		return ERR_CAST(tmp);
 	}
 
 	for (i = 0; i < rm->data.op_nents; ++i) {
-- 
2.25.1