fs: validate position argument before length === 0 early return by geeksilva97 · Pull Request #62674 · nodejs/node

fs.read() and fs.readSync() validate the `position` argument via
validatePosition() (tightened in commit ed05549). The symmetric
write path was never updated: fs.write(), fs.writeSync() and
fsPromises.FileHandle.write() silently coerced any non-number
`position` (strings, objects, booleans, NaN, out-of-range numbers,
out-of-range bigints) to `null`, which means "use the current file
offset".

Impact: callers relying on an ERR_OUT_OF_RANGE / ERR_INVALID_ARG_TYPE
throw to reject malformed inputs instead silently got a stream-mode
write at the current file offset — bypassing validation and
potentially overwriting file content the caller thought it had
refused. Inconsistent between read and write is a direct input-
validation failure that is trivially triggerable from userland:

    fs.writeSync(fd, Buffer.from('PWN'), 0, 3, -2);      // accepted
    fs.writeSync(fd, Buffer.from('PWN'), 0, 3, 'str');   // accepted
    fs.writeSync(fd, Buffer.from('PWN'), 0, 3, { not: 'num' }); // accepted

Mirror the read-side validation in all three write entry points, add
a regression test covering positional-arg, options-object and
mutation-guarded-options-object invocations for sync, async and
promise variants.

Refs: nodejs#62674