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  > > > Rich > >  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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