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Message-ID: <CAK-_uh655WeD52j426MnxGG1F6N-MW3OtkHMsSzEnhf5suxSsw@mail.gmail.com>
Date: Fri, 24 Feb 2023 09:42:00 -0500
From: Tamir Duberstein <tamird@...gle.com>
To: NRK <nrk@...root.org>
Cc: Rich Felker <dalias@...c.org>, musl@...ts.openwall.com
Subject: Re: undefined behavior in fread.c
We could take the lock and still avoid UB with an early return.
On Fri, Feb 24, 2023, 09:17 NRK <nrk@...root.org> wrote:
> On Fri, Feb 24, 2023 at 09:07:41AM -0500, Rich Felker wrote:
> > stdio functions are required (by POSIX) to behave as if they take a
> > mutex on the FILE. If fread with a length of zero makes forward
> > progress when another thread holds the lock, this is non-conforming.
>
> OK, I see. Wasn't aware of that.
>
> On a sidenote, if I'm reading the right function (libio/iofread.c) then
> glibc is taking the lock _after_ they do the size check.
>
> if (bytes_requested == 0)
> return 0;
> _IO_acquire_lock (fp);
> /* ... */
>
> - NRK
>
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