From: Rich Felker <dalias@libc.org>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Cc: libc-alpha@sourceware.org, Florian Weimer <fweimer@redhat.com>
Subject: Re: [PATCH v8 0/7] Add pidfd and cgroupv2 support for process creation
Date: Fri, 18 Aug 2023 13:51:50 -0400 [thread overview]
Message-ID: <20230818175149.GA25836@brightrain.aerifal.cx> (raw)
In-Reply-To: <20230818140642.1623571-1-adhemerval.zanella@linaro.org>
On Fri, Aug 18, 2023 at 11:06:35AM -0300, Adhemerval Zanella via Libc-alpha wrote:
> The glibc 2.36 added wrappers for Linux syscall pidfd_open, pidfd_getfd,
> and pidfd_send_signal, and exported the P_PIDFD to use along with
> waitid. The pidfd is a race-free interface, however, the pidfd_open is
> subject to TOCTOU if the file descriptor is not obtained directly from
> the clone or clone3 syscall (there is still a small window between the
> clone return and the pidfd_getfd where the process can be reaped and the
> process ID reused).
Unless I'm missing something, that window is purely programmer error.
The pid belongs to the parent process, that called fork, posix_spawn,
clone, or whatever, and is responsible for not freeing it until it's
done using it.
Yes this can happen if you install a SIGCHLD handler that reaps
anything it sees, or if you're calling wait without a pid. This is
programming error. If you're stuck with code outside your control that
makes that mistake, you can already avoid it with clone by setting the
child exit signal to 0 rather than SIGCHLD. But it's best just not to
do that.
IMO making a new, complex, highly nonstandard interface to work around
a problem that's programmer error, and getting this nonstandard and
nonportable pattern into mainstream software, has negative value.
Rich
next prev parent reply other threads:[~2023-08-18 17:51 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-18 14:06 Adhemerval Zanella
2023-08-18 14:06 ` [PATCH v8 1/7] arm: Add the clone3 wrapper Adhemerval Zanella
2023-08-18 14:06 ` [PATCH v8 2/7] mips: " Adhemerval Zanella
2023-08-18 14:06 ` [PATCH v8 3/7] linux: Define __ASSUME_CLONE3 to 0 for alpha, ia64, nios2, sh, and sparc Adhemerval Zanella
2023-08-24 6:06 ` Florian Weimer
2023-08-18 14:06 ` [PATCH v8 4/7] linux: Add posix_spawnattr_{get,set}cgroup_np (BZ 26731) Adhemerval Zanella
2023-08-24 7:00 ` Florian Weimer
2023-08-18 14:06 ` [PATCH v8 5/7] posix: Add pidfd_spawn and pidfd_spawnp (BZ 30349) Adhemerval Zanella
2023-08-24 7:13 ` Florian Weimer
2023-08-24 15:43 ` Adhemerval Zanella Netto
2023-08-24 17:00 ` Florian Weimer
2023-08-24 17:10 ` Adhemerval Zanella Netto
2023-08-24 18:18 ` Florian Weimer
2023-08-24 18:22 ` Adhemerval Zanella Netto
2023-08-25 10:38 ` Florian Weimer
2023-08-25 16:37 ` Adhemerval Zanella Netto
2023-08-18 14:06 ` [PATCH v8 6/7] posix: Add fork_np (BZ 26371) Adhemerval Zanella
2023-08-24 6:07 ` Florian Weimer
2023-08-18 14:06 ` [PATCH v8 7/7] linux: Add pidfd_getpid Adhemerval Zanella
2023-08-24 7:53 ` Florian Weimer
2023-08-18 17:51 ` Rich Felker [this message]
2023-08-18 18:34 ` [PATCH v8 0/7] Add pidfd and cgroupv2 support for process creation Adhemerval Zanella Netto
2023-08-28 12:52 ` Luca Boccassi
2023-08-28 13:21 ` Florian Weimer
2023-08-28 13:50 ` Luca Boccassi
2023-08-21 6:53 ` Florian Weimer
2023-08-21 13:55 ` Rich Felker
2023-08-24 7:25 ` Florian Weimer
2023-08-24 12:21 ` Rich Felker
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