netdev - [PATCH 2/3] xfrm/compat: memset(0) 64-bit padding at right place

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Date:   Fri, 30 Oct 2020 02:25:59 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Hillf Danton <hdanton@...a.com>, netdev@...r.kernel.org,
        syzbot+c43831072e7df506a646@...kaller.appspotmail.com
Subject: [PATCH 2/3] xfrm/compat: memset(0) 64-bit padding at right place

32-bit messages translated by xfrm_compat can have attributes attached.
For all, but XFRMA_SA, XFRMA_POLICY the size of payload is the same
in 32-bit UABI and 64-bit UABI. For XFRMA_SA (struct xfrm_usersa_info)
and XFRMA_POLICY (struct xfrm_userpolicy_info) it's only tail-padding
that is present in 64-bit payload, but not in 32-bit.
The proper size for destination nlattr is already calculated by
xfrm_user_rcv_calculate_len64() and allocated with kvmalloc().

xfrm_attr_cpy32() copies 32-bit copy_len into 64-bit attribute
translated payload, zero-filling possible padding for SA/POLICY.
Due to a typo, *pos already has 64-bit payload size, in a result next
memset(0) is called on the memory after the translated attribute, not on
the tail-padding of it.

Reported-by: syzbot+c43831072e7df506a646@...kaller.appspotmail.com
Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
 net/xfrm/xfrm_compat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_compat.c b/net/xfrm/xfrm_compat.c
index 17edbf935e35..556e9f33b815 100644
--- a/net/xfrm/xfrm_compat.c
+++ b/net/xfrm/xfrm_compat.c
@@ -388,7 +388,7 @@ static int xfrm_attr_cpy32(void *dst, size_t *pos, const struct nlattr *src,

 	memcpy(nla, src, nla_attr_size(copy_len));
 	nla->nla_len = nla_attr_size(payload);
-	*pos += nla_attr_size(payload);
+	*pos += nla_attr_size(copy_len);
 	nlmsg->nlmsg_len += nla->nla_len;

 	memset(dst + *pos, 0, payload - copy_len);
-- 
2.28.0