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Date: Sat, 27 Feb 2021 12:35:04 -0500
From: Rich Felker <dalias@...c.org>
To: Khem Raj <raj.khem@...il.com>
Cc: musl@...ts.openwall.com, Dominic Chen <d.c.ddcc@...il.com>
Subject: Re: fdopen() doesn't check for valid fd
On Sat, Feb 27, 2021 at 09:13:17AM -0800, Khem Raj wrote:
> On Fri, Feb 26, 2021 at 10:01 AM Rich Felker <dalias@...c.org> wrote:
> >
> > On Fri, Feb 26, 2021 at 12:36:19PM -0500, Dominic Chen wrote:
> > > I've been verifying the behavior of an application between glibc and
> > > musl, and have noticed that the musl implementation of fdopen()
> > > assumes that the input fd is valid, whereas glibc does not. Per
> > > https://pubs.opengroup.org/onlinepubs/9699919799/, it seems that
> > > fdopen() is allowed to fail with EBADF, so inside __fdopen(), the
> > > syscalls to SYS_fcntl and SYS_ioctl should probably check for an
> > > error, deallocate the FILE *, and return nullptr.
> >
> > This is specified as a "may fail" error not a "shall fail". It was
> > discussed before (I can look up the old thread if you're interested)
> > and there are some paths in which checking for it would be free, but
> > others where it would not, and it would require reorganizing the
> > function's flow in a way that's less desirable in one way or another,
> > so it doesn't seem like a good idea for the sake of something a caller
> > can't actually use.
> >
>
> perhaps we should add it to differences with glibc document [1]
>
> > Rich
>
> [1] https://wiki.musl-libc.org/functional-differences-from-glibc.html
I'm not fundmanetally opposed to that, but it should probably be a
more general statement about "may fail" and UB; otherwise we'd end up
documenting a very large number of little details like this one.
Rich
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