Re: [RFC v1] man/man2/close.2: CAVEATS: Document divergence from POSIX.1-2024

On Sat, Jan 24, 2026 at 08:34:01PM +0100, The 8472 wrote:

On 23/01/2026 01:33, Zack Weinberg wrote:

[...]

quoted

ERRORS
        EBADF  The fd argument was not a valid, open file descriptor.

Unfortunately EBADF from FUSE is passed through unfiltered by the kernel
on close[0], that makes it more difficult to reliably detect bugs relating
to double-closes of file descriptors.

Wow, that's a nasty bug. Are the kernel folks not amenable to fixing
it? I wonder if that could even have security implications. I think
you could detect these fraudulent EBADFs (albeit not under conditions
where there's a race bug) by performing fcntl/F_GETFD before close and
knowing the EBADF from close is fake is fcntl didn't EBADF, but that
seems like an unreasonable cost to work around FUSE behaving badly.

Rich