netdev - [PATCH net] sctp: check stream reset info len before making reconf chunk

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Date:   Mon, 13 Nov 2017 13:39:27 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org
Cc:     davem@...emloft.net,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, syzkaller@...glegroups.com
Subject: [PATCH net] sctp: check stream reset info len before making reconf chunk

Now when resetting stream, if both in and out flags are set, the info
len can reach:
  sizeof(struct sctp_strreset_outreq) + SCTP_MAX_STREAM(65535) +
  sizeof(struct sctp_strreset_inreq)  + SCTP_MAX_STREAM(65535)
even without duplicated stream no, this value is far greater than the
chunk's max size.

_sctp_make_chunk doesn't do any check for this, which would cause the
skb it allocs is huge, syzbot even reported a crash due to this.

This patch is to check stream reset info len before making reconf
chunk and return NULL if the len exceeds chunk's capacity.

Fixes: cc16f00f6529 ("sctp: add support for generating stream reconf ssn reset request chunk")
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 net/sctp/sm_make_chunk.c | 7 +++++--
 net/sctp/stream.c        | 8 +++++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 514465b..a21328a 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -3598,14 +3598,17 @@ struct sctp_chunk *sctp_make_strreset_req(
 	__u16 stream_len = stream_num * 2;
 	struct sctp_strreset_inreq inreq;
 	struct sctp_chunk *retval;
-	__u16 outlen, inlen;
+	int outlen, inlen;
 
 	outlen = (sizeof(outreq) + stream_len) * out;
 	inlen = (sizeof(inreq) + stream_len) * in;
 
+	if (outlen + inlen > SCTP_MAX_CHUNK_LEN - sizeof(struct sctp_chunkhdr))
+		return ERR_PTR(-EINVAL);
+
 	retval = sctp_make_reconf(asoc, outlen + inlen);
 	if (!retval)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	if (outlen) {
 		outreq.param_hdr.type = SCTP_PARAM_RESET_OUT_REQUEST;
diff --git a/net/sctp/stream.c b/net/sctp/stream.c
index fa8371f..51a25bf 100644
--- a/net/sctp/stream.c
+++ b/net/sctp/stream.c
@@ -162,8 +162,8 @@ int sctp_send_reset_streams(struct sctp_association *asoc,
 
 	kfree(nstr_list);
 
-	if (!chunk) {
-		retval = -ENOMEM;
+	if (IS_ERR(chunk)) {
+		retval = PTR_ERR(chunk);
 		goto out;
 	}
 
@@ -482,8 +482,10 @@ struct sctp_chunk *sctp_process_strreset_inreq(
 	}
 
 	chunk = sctp_make_strreset_req(asoc, nums, str_p, 1, 0);
-	if (!chunk)
+	if (IS_ERR(chunk)) {
+		chunk = NULL;
 		goto out;
+	}
 
 	if (nums)
 		for (i = 0; i < nums; i++)
-- 
2.1.0