Depending on how it's handled, there may not be any legal violation.
Congress has the constitutional right of oversight of the Executive Branch, but an unredacted report would have to be handled with kid gloves, which can be done by having it sent to either the House Judiciary Committee or the House Intelligence Committee, either one's sessions being held in private. Previous sensitive intelligence reports were available for congressional scrutiny, including Whitewater, Watergate, and some of the Benghazi hearings, so there is ample precedent for this approach.
And also just a reminder that Trump said he wanted it all to come out as well as every single representative in the House including the Pubs. Even now Trump could issue an order for full public release of the report if he wanted to, which would then be legal without question.
It is clear, however, that both the Trump camp and also many of the Republicans don't want it entirely released, and I do believe most here well know why that's likely to be the case. There's a reason why Trump and the Senate Republicans wanted Barr in as AG. But by trying to stonewall it, this may very well drag all this out until next year and keeping this all in the spotlight. Most Americans when polled want it released to the public, not just Congress, and I don't think responsible people will be satisfied if the Pubs stonewall its release after some bipartisan redaction. It's like "What are you hiding and why are you hiding something we paid for?".
Seems to me that a true conservative would want this released to Congress (unredacted) and to the public (redacted), especially since we paid for it.