2021-06-25 10:25:15

by Pavel Skripkin

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: [email protected]
Signed-off-by: Pavel Skripkin <[email protected]>
---

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

2021-06-30 06:51:59

by Steffen Klassert

Subject: Re: [PATCH] net: xfrm: fix memory leak in xfrm_user_rcv_msg

On Fri, Jun 25, 2021 at 01:23:54PM +0300, Pavel Skripkin wrote:
> 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: [email protected]
> Signed-off-by: Pavel Skripkin <[email protected]>

Applied, thanks a lot!