Subject: [PATCH 3/8] xfrm: fix uctx len check in verify_sec_ctx_len

From: Steffen Klassert <[email-masked]>
Date: Fri, 27 Mar 2020 09:10:02 +0100

From: Xin Long <[email-masked]>

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 <[email-masked]>
Signed-off-by: Steffen Klassert <[email-masked]>
---
 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 b88ba45ff1ac..38ff02d31402 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;
-- 
2.17.1