file: fix close_range() for unshare+cloexec
syzbot reported a bug when putting the last reference to a tasks file descriptor table. Debugging this showed we didn't recalculate the current maximum fd number for CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC after we unshared the file descriptors table. So max_fd could exceed the current fdtable maximum causing us to set excessive bits. As a concrete example, let's say the user requested everything from fd 4 to ~0UL to be closed and their current fdtable size is 256 with their highest open fd being 4. With CLOSE_RANGE_UNSHARE the caller will end up with a new fdtable which has room for 64 file descriptors since that is the lowest fdtable size we accept. But now max_fd will still point to 255 and needs to be adjusted. Fix this by retrieving the correct maximum fd value in __range_cloexec(). Reported-by:<syzbot+283ce5a46486d6acdbaf@syzkaller.appspotmail.com> Fixes: 582f1fb6 ("fs, close_range: add flag CLOSE_RANGE_CLOEXEC") Fixes: fec8a6a6 ("close_range: un...
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