netdev - [PATCH ipsec] xfrm: fix uctx len check in verify_sec_ctx

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Message-Id: <afee25abdf818c7a7374773a6f347cf5c719038e.1581254129.git.lucien.xin@gmail.com>
Date:   Sun,  9 Feb 2020 21:15:29 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     netdev@...r.kernel.org
Cc:     Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Trent Jaeger <tjaeger@....psu.edu>,
        Jamal Hadi Salim <hadi@...erus.ca>,
        Sabrina Dubroca <sd@...asysnail.net>
Subject: [PATCH ipsec] xfrm: fix uctx len check in verify_sec_ctx_len

It's not sufficient to do 'uctx->len != (sizeof(struct xfrm_user_sec_ctx) +
uctx->ctx_len)' check only, as uctx->len may be greater than nla_len(rt),
in which case it will cause slab-out-of-bounds when accessing uctx->ctx_str
later.

This patch is to fix it by return -EINVAL when uctx->len > nla_len(rt).

Fixes: df71837d5024 ("[LSM-IPSec]: Security association restriction.")
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 net/xfrm/xfrm_user.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index b88ba45..38ff02d 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -110,7 +110,8 @@ static inline int verify_sec_ctx_len(struct nlattr **attrs)
 		return 0;
 
 	uctx = nla_data(rt);
-	if (uctx->len != (sizeof(struct xfrm_user_sec_ctx) + uctx->ctx_len))
+	if (uctx->len > nla_len(rt) ||
+	    uctx->len != (sizeof(struct xfrm_user_sec_ctx) + uctx->ctx_len))
 		return -EINVAL;
 
 	return 0;
-- 
2.1.0