What version of Go are you using (go version)?

The problem is obvious from inspection of the source code and the documented Linux getrandom semantics, I looked at master.

What operating system and processor architecture are you using (go env)?

This affects all Linux platforms with support for the getrandom() system call.

What did you do?

Looked at the code to see if crypto/rand was correct or not.

What did you expect to see?

getrandom() used correctly.

What did you see instead?

From the getrandom documentation:

When reading from the urandom source, a maximum of 33554431 bytes is returned by a single call to getrandom() on systems where int has a size of 32 bits.

From the system call implementation in drivers/char/random.c:

	if (count > INT_MAX)
		count = INT_MAX;

src/crypto/rand/rand_linux.go:getRandomLinux() will return false due to the truncated getrandom() output, and the caller will fall back to servicing the request by opening and reading from /dev/urandom.

While I would be inclined to agree that a Read that is 32 MiB - 1 bytes or larger is excessive and out of the ordinary, this still should be handled correctly or documented.