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Message-ID: <35c9d22e-7c52-4dfe-b58e-a22c2b4a933f@gmail.com>
Date: Fri, 12 Sep 2025 21:40:22 -0400
From: Demi Marie Obenour <demiobenour@...il.com>
To: musl@...ts.openwall.com
Subject: closefrom and close_range wrappers
Would it make sense for musl to provide close_range and
closefrom? The main uses of them are to close unwanted
FDs after a fork and before exec. close_range() can also
be used to mark them close-on-exec instead.
The main advantage of closefrom() is that it is portable
to more systems. Closing file descriptors one doesn't own
is not an issue because the code that does own these FDs
will never get a chance to run. In particular, calling any
stdio functions that use anything but stdin, stdout, and
stderr would be UB. stdin, stdout, and stderr use FD 0, 1,
and 2, respectively, and those are almost always left open.
Yes, this is all a consequence of fork()/exec() being an
extremely poor API, but I don't know of a better solution.
There are third-party libraries (including glib and wlroots)
that expect one to either use an API like this or emulate it
by scanning /proc/self/fd (yuck). Yes, these libraries should
be atomically setting O_CLOEXEC, but their authors disagree
and maintaining downstream forks is not practical.
--
Sincerely,
Demi Marie Obenour (she/her/hers)
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