[PATCH v2] net/rds: Fix a use after free in rds_message_map_pages

[Lv Yunlong]

In rds_message_map_pages, the rm is freed by rds_message_put(rm).
But rm is still used by rm->data.op_sg in return value.

My patch assigns ERR_CAST(rm->data.op_sg) to err before the rm is
freed to avoid the uaf.

Fixes: 7dba92037baf3 ("net/rds: Use ERR_PTR for rds_message_alloc_sgs()")
Signed-off-by: Lv Yunlong <lyl2...@mail.ustc.edu.cn>
---
 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..799034e0f513 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)) {
+               void *err = ERR_CAST(rm->data.op_sg);
                rds_message_put(rm);
-               return ERR_CAST(rm->data.op_sg);
+               return err;
        }
 
        for (i = 0; i < rm->data.op_nents; ++i) {
-- 
2.25.1