linux-kernel - [PATCH] cxgb4: fix undefined behavior in mem.c

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Date:   Thu, 28 Feb 2019 15:38:38 -0700
From:   Shaobo He <shaobo@...utah.edu>
To:     linux-rdma@...r.kernel.org
Cc:     shaobo@...utah.edu, Steve Wise <swise@...lsio.com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] cxgb4: fix undefined behavior in mem.c

In function `c4iw_dealloc_mw`, variable mhp's value is printed after
freed, which triggers undefined behavior according to this post:
https://trust-in-soft.com/dangling-pointer-indeterminate/.

This commit fixes it by swapping the order of `kfree` and `pr_debug`.

Signed-off-by: Shaobo He <shaobo@...utah.edu>
---
 drivers/infiniband/hw/cxgb4/mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/cxgb4/mem.c b/drivers/infiniband/hw/cxgb4/mem.c
index 7b76e6f..bb8e0bc 100644
--- a/drivers/infiniband/hw/cxgb4/mem.c
+++ b/drivers/infiniband/hw/cxgb4/mem.c
@@ -684,8 +684,8 @@ int c4iw_dealloc_mw(struct ib_mw *mw)
 			  mhp->wr_waitp);
 	kfree_skb(mhp->dereg_skb);
 	c4iw_put_wr_wait(mhp->wr_waitp);
-	kfree(mhp);
 	pr_debug("ib_mw %p mmid 0x%x ptr %p\n", mw, mmid, mhp);
+	kfree(mhp);
 	return 0;
 }
 
-- 
2.7.4