linux-kernel - [PATCH] xfrm/compat: Cleanup WARN()s that can be user-triggered

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Date:   Tue, 30 Mar 2021 00:25:06 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        syzbot+834ffd1afc7212eb8147@...kaller.appspotmail.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Jakub Kicinski <kuba@...nel.org>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        netdev@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH] xfrm/compat: Cleanup WARN()s that can be user-triggered

Replace WARN_ONCE() that can be triggered from userspace with
pr_warn_once(). Those still give user a hint what's the issue.

I've left WARN()s that are not possible to trigger with current
code-base and that would mean that the code has issues:
- relying on current compat_msg_min[type] <= xfrm_msg_min[type]
- expected 4-byte padding size difference between
  compat_msg_min[type] and xfrm_msg_min[type]
- compat_policy[type].len <= xfrma_policy[type].len
(for every type)

Reported-by: syzbot+834ffd1afc7212eb8147@...kaller.appspotmail.com
Fixes: 5f3eea6b7e8f ("xfrm/compat: Attach xfrm dumps to 64=>32 bit translator")
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Steffen Klassert <steffen.klassert@...unet.com>
Cc: netdev@...r.kernel.org
Cc: stable@...r.kernel.org
Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
 net/xfrm/xfrm_compat.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/xfrm/xfrm_compat.c b/net/xfrm/xfrm_compat.c
index d8e8a11ca845..a20aec9d7393 100644
--- a/net/xfrm/xfrm_compat.c
+++ b/net/xfrm/xfrm_compat.c
@@ -216,7 +216,7 @@ static struct nlmsghdr *xfrm_nlmsg_put_compat(struct sk_buff *skb,
 	case XFRM_MSG_GETSADINFO:
 	case XFRM_MSG_GETSPDINFO:
 	default:
-		WARN_ONCE(1, "unsupported nlmsg_type %d", nlh_src->nlmsg_type);
+		pr_warn_once("unsupported nlmsg_type %d\n", nlh_src->nlmsg_type);
 		return ERR_PTR(-EOPNOTSUPP);
 	}
 
@@ -277,7 +277,7 @@ static int xfrm_xlate64_attr(struct sk_buff *dst, const struct nlattr *src)
 		return xfrm_nla_cpy(dst, src, nla_len(src));
 	default:
 		BUILD_BUG_ON(XFRMA_MAX != XFRMA_IF_ID);
-		WARN_ONCE(1, "unsupported nla_type %d", src->nla_type);
+		pr_warn_once("unsupported nla_type %d\n", src->nla_type);
 		return -EOPNOTSUPP;
 	}
 }
@@ -315,8 +315,10 @@ static int xfrm_alloc_compat(struct sk_buff *skb, const struct nlmsghdr *nlh_src
 	struct sk_buff *new = NULL;
 	int err;
 
-	if (WARN_ON_ONCE(type >= ARRAY_SIZE(xfrm_msg_min)))
+	if (type >= ARRAY_SIZE(xfrm_msg_min)) {
+		pr_warn_once("unsupported nlmsg_type %d\n", nlh_src->nlmsg_type);
 		return -EOPNOTSUPP;
+	}
 
 	if (skb_shinfo(skb)->frag_list == NULL) {
 		new = alloc_skb(skb->len + skb_tailroom(skb), GFP_ATOMIC);
@@ -378,6 +380,10 @@ static int xfrm_attr_cpy32(void *dst, size_t *pos, const struct nlattr *src,
 	struct nlmsghdr *nlmsg = dst;
 	struct nlattr *nla;
 
+	/* xfrm_user_rcv_msg_compat() relies on fact that 32-bit messages
+	 * have the same len or shorted than 64-bit ones.
+	 * 32-bit translation that is bigger than 64-bit original is unexpected.
+	 */
 	if (WARN_ON_ONCE(copy_len > payload))
 		copy_len = payload;
 
-- 
2.31.0