On Tue, Nov 14, 2017 at 3:54 AM, Marcelo Ricardo Leitner
<marcelo.leitner@xxxxxxxxx> wrote:
> On Mon, Nov 13, 2017 at 11:15:40PM +0800, Xin Long wrote:
>> On Mon, Nov 13, 2017 at 11:09 PM, Neil Horman <nhorman@xxxxxxxxxxxxx> wrote:
>> > On Mon, Nov 13, 2017 at 01:39:27PM +0800, Xin Long wrote:
>> >> 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@xxxxxxxxxx>
>> >> Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
>> >> ---
>> >> 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;
>
> Unrelated, but.. won't stream_len overflow if stream_num >= 32768?
> When called form sctp_send_reset_streams() I don't see anything
> restricting it to such range.
right.
>
>> >> 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);
>> >> +
>> > Why all the ERR_PTR manipulations here? Just returning NULL, like the fuction
>> > has been doing is sufficient to set ENOMEM at both call sites
>> I don't like ERR_PTR handling here either,
>> But it shouldn't be ENOMEM, should it ?
>>
>> It may confuse users, but I'm also ok to let it just return
>> ENOMEM as you wish. wdyt ?
>
> Returning ENOMEM in the above error can be misleading. It's not that
> we cannot allocate it, it's that it won't fit the packet no matter how
> much memory we add to the system.
right.
let's move the check into sctp_send_reset_streams()
I believe this one fixes them both:
@@ -139,15 +139,31 @@ int sctp_send_reset_streams(struct sctp_association *asoc,
str_nums = params->srs_number_streams;
str_list = params->srs_stream_list;
- if (out && str_nums)
- for (i = 0; i < str_nums; i++)
- if (str_list[i] >= stream->outcnt)
- goto out;
+ if (str_nums) {
+ int param_len = 0;
- if (in && str_nums)
- for (i = 0; i < str_nums; i++)
- if (str_list[i] >= stream->incnt)
- goto out;
+ if (out) {
+ for (i = 0; i < str_nums; i++)
+ if (str_list[i] >= stream->outcnt)
+ goto out;
+
+ param_len = str_nums * 2 +
+ sizeof(struct sctp_strreset_outreq);
+ }
+
+ if (in) {
+ for (i = 0; i < str_nums; i++)
+ if (str_list[i] >= stream->incnt)
+ goto out;
+
+ param_len += str_nums * 2 +
+ sizeof(struct sctp_strreset_inreq);
+ }
+
+ if (param_len > SCTP_MAX_CHUNK_LEN -
+ sizeof(struct sctp_reconf_chunk))
+ goto out;
+ }
and int this fix, it's good to do all checks only when str_nums !=0.
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