netdev - [PATCH v3 1/1] xdp: avoid calling kfree twice

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Message-Id: <20201211042610.71081-1-yanjun.zhu@intel.com>
Date:   Thu, 10 Dec 2020 23:26:10 -0500
From:   Zhu Yanjun <yanjun.zhu@...el.com>
To:     zyjzyj2000@...il.com, bjorn.topel@...el.com,
        magnus.karlsson@...el.com, netdev@...r.kernel.org,
        jonathan.lemon@...il.com
Cc:     Zhu Yanjun <yanjun.zhu@...el.com>, Ye Dong <dong.ye@...el.com>
Subject: [PATCH v3 1/1] xdp: avoid calling kfree twice

In the function xdp_umem_pin_pages, if npgs != umem->npgs and
npgs >= 0, the function xdp_umem_unpin_pages is called. In this
function, kfree is called to handle umem->pgs, and then in the
function xdp_umem_pin_pages, kfree is called again to handle
umem->pgs. Eventually, to umem->pgs, kfree is called twice.

Since umem->pgs is set to NULL after the first kfree, the second
kfree would not trigger call trace.

Fixes: c0c77d8fb787 ("xsk: add user memory registration support sockopt")
CC: Ye Dong <dong.ye@...el.com>
Acked-by: Björn Töpel <bjorn.topel@...el.com>
Signed-off-by: Zhu Yanjun <yanjun.zhu@...el.com>
---
 net/xdp/xdp_umem.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
index 56a28a686988..01b31c56cead 100644
--- a/net/xdp/xdp_umem.c
+++ b/net/xdp/xdp_umem.c
@@ -97,7 +97,6 @@ static int xdp_umem_pin_pages(struct xdp_umem *umem, unsigned long address)
 {
 	unsigned int gup_flags = FOLL_WRITE;
 	long npgs;
-	int err;
 
 	umem->pgs = kcalloc(umem->npgs, sizeof(*umem->pgs),
 			    GFP_KERNEL | __GFP_NOWARN);
@@ -112,20 +111,14 @@ static int xdp_umem_pin_pages(struct xdp_umem *umem, unsigned long address)
 	if (npgs != umem->npgs) {
 		if (npgs >= 0) {
 			umem->npgs = npgs;
-			err = -ENOMEM;
-			goto out_pin;
+			xdp_umem_unpin_pages(umem);
+			return -ENOMEM;
 		}
-		err = npgs;
-		goto out_pgs;
+		kfree(umem->pgs);
+		umem->pgs = NULL;
+		return (int)npgs;
 	}
 	return 0;
-
-out_pin:
-	xdp_umem_unpin_pages(umem);
-out_pgs:
-	kfree(umem->pgs);
-	umem->pgs = NULL;
-	return err;
 }
 
 static int xdp_umem_account_pages(struct xdp_umem *umem)
-- 
2.18.4