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

[Xin Long]

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 <dvyu...@google.com>
Signed-off-by: Xin Long <lucien....@gmail.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