netdev - [PATCH] net: xfrm: fix memory leak in xfrm_user_rcv

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Message-Id: <20210625102354.18266-1-paskripkin@gmail.com>
Date:   Fri, 25 Jun 2021 13:23:54 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     steffen.klassert@...unet.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, 0x7f454c46@...il.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Pavel Skripkin <paskripkin@...il.com>,
        syzbot+fb347cf82c73a90efcca@...kaller.appspotmail.com
Subject: [PATCH] net: xfrm: fix memory leak in xfrm_user_rcv_msg

Syzbot reported memory leak in xfrm_user_rcv_msg(). The
problem was is non-freed skb's frag_list.

In skb_release_all() skb_release_data() will be called only
in case of skb->head != NULL, but netlink_skb_destructor()
sets head to NULL. So, allocated frag_list skb should be
freed manualy, since consume_skb() won't take care of it

Fixes: 5106f4a8acff ("xfrm/compat: Add 32=>64-bit messages translator")
Reported-and-tested-by: syzbot+fb347cf82c73a90efcca@...kaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
---

One thing I'm not sure about is did I choose the rigth
place to free this skb, maybe we can move this clean up
a little bit deeper, like in xfrm_alloc_userspi()?

---
 net/xfrm/xfrm_user.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index f0aecee4d539..ff60ff804074 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2811,6 +2811,16 @@ static int xfrm_user_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	err = link->doit(skb, nlh, attrs);
 
+	/* We need to free skb allocated in xfrm_alloc_compat() before
+	 * returning from this function, because consume_skb() won't take
+	 * care of frag_list since netlink destructor sets
+	 * sbk->head to NULL. (see netlink_skb_destructor())
+	 */
+	if (skb_has_frag_list(skb)) {
+		kfree_skb(skb_shinfo(skb)->frag_list);
+		skb_shinfo(skb)->frag_list = NULL;
+	}
+
 err:
 	kvfree(nlh64);
 	return err;
-- 
2.32.0