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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Xin Long <lucien.xin@gmail.com>,
        Steffen Klassert <steffen.klassert@secunet.com>
Subject: [PATCH 5.5 127/170] xfrm: fix uctx len check in verify_sec_ctx_len
Date:   Tue, 31 Mar 2020 10:59:01 +0200
Message-Id: <20200331085437.322425434@linuxfoundation.org>
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From: Xin Long <lucien.xin@gmail.com>

commit 171d449a028573b2f0acdc7f31ecbb045391b320 upstream.

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@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/xfrm/xfrm_user.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -110,7 +110,8 @@ static inline int verify_sec_ctx_len(str
 		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;