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From:   Lv Yunlong <lyl2019@mail.ustc.edu.cn>
To:     santosh.shilimkar@oracle.com, davem@davemloft.net, kuba@kernel.org
Cc:     netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
        rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org,
        Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Subject: [PATCH v2] net/rds: Fix a use after free in rds_message_map_pages
Date:   Tue, 30 Mar 2021 18:59:59 -0700
Message-Id: <20210331015959.4404-1-lyl2019@mail.ustc.edu.cn>
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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 <lyl2019@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