Re: [PATCH net] sctp: make sure stream nums can match optlen in sctp_setsockopt_reset_streams
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From: Neil Horman <nhorman@tuxdriver.com>
Date: 2017-12-11 14:55:12
Also in:
linux-sctp
On Sun, Dec 10, 2017 at 03:40:51PM +0800, Xin Long wrote:
quoted hunk ↗ jump to hunk
Now in sctp_setsockopt_reset_streams, it only does the check optlen < sizeof(*params) for optlen. But it's not enough, as params->srs_number_streams should also match optlen. If the streams in params->srs_stream_list are less than stream nums in params->srs_number_streams, later when dereferencing the stream list, it could cause a slab-out-of-bounds crash, as reported by syzbot. This patch is to fix it by also checking the stream numbers in sctp_setsockopt_reset_streams to make sure at least it's not greater than the streams in the list. Fixes: 7f9d68ac944e ("sctp: implement sender-side procedures for SSN Reset Request Parameter") Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Xin Long <lucien.xin@gmail.com> --- net/sctp/socket.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)diff --git a/net/sctp/socket.c b/net/sctp/socket.c index 014847e..dbf140d 100644 --- a/net/sctp/socket.c +++ b/net/sctp/socket.c@@ -3891,13 +3891,17 @@ static int sctp_setsockopt_reset_streams(struct sock *sk, struct sctp_association *asoc; int retval = -EINVAL; - if (optlen < sizeof(struct sctp_reset_streams)) + if (optlen < sizeof(*params)) return -EINVAL;
Is this going to work in all corner cases? IIRC struct sctp_reset_stream has variable length array at the end of it, and so sizeof(struct sctp_reset_streams) returns just the size of the struct, while sizeof(*params) returns the size of the entire object (including the array elements). If a user space task allocates a static memory block to hold this struct and the array, and passes it in with a shorter optlen (if for example, they do not intend to use all the array elements), this will cause a failure, where no failure is truly warranted. It seems the correct check to me should be the origional sizeof(struct sctp_reset_streams) check, and the below check to ensure that there are at least the same number of array elements available as indicated in srs_nuber_streams. Regards Neil
params = memdup_user(optval, optlen); if (IS_ERR(params)) return PTR_ERR(params); + if (params->srs_number_streams * sizeof(__u16) > + optlen - sizeof(*params)) + goto out; + asoc = sctp_id2assoc(sk, params->srs_assoc_id); if (!asoc) goto out; -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html