0005568: Unix.open_flag lacks O_CLOEXEC

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Date Submitted

Last Update

0005568

OCaml

OCaml otherlibs

public

2012-03-30 23:44

2012-08-06 18:33

Reporter

goswin

Assigned To

Priority

normal

Severity

minor

Reproducibility

always

Status

acknowledged

Resolution

open

Platform

Linux

OS Version

Product Version

3.12.1

Target Version

4.01.0+dev

Fixed in Version

Summary

0005568: Unix.open_flag lacks O_CLOEXEC

Description

       O_CLOEXEC (Since Linux 2.6.23)
              Enable the close-on-exec flag for the new file descriptor.
              Specifying this flag permits a program to avoid additional
              fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Addi-
              tionally, use of this flag is essential in some multithreaded
              programs since using a separate fcntl(2) F_SETFD operation to
              set the FD_CLOEXEC flag does not suffice to avoid race condi-
              tions where one thread opens a file descriptor at the same time
              as another thread does a fork(2) plus execve(2).

There also some other flags missing but O_CLOEXEC has serious security implications.

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Attached Files

Relationships

related to	0005256	feedback		Processes opened using Unix.open_process* inherit all opened file descriptors (including sockets)
child of	0005569	resolved		missing Unix.dup_cloexec, Unix.get_cloexec and Unix.set_cloexec

Notes
(0007256) doligez (manager) 2012-04-01 00:30	See note in PR#5569.

(0007260) gerd (reporter) 2012-04-02 10:47	I support this because it avoids a race condition between opening a file and executing a command in a multi-threaded app. If you don't open with O_CLOEXEC, it can happen that the exec() is done between open() and the fcntl() setting the flag, and the file remains open in the child process. See also PR#5256. O_CLOEXEC is covered by POSIX. Of course, this is only a partial solution to the mentioned problem, but this not our issue, but POSIX': The other syscalls creating file descriptors don't have an O_CLOEXEC flag.

(0007270) goswin (reporter) 2012-04-03 15:28	I would rather consider this a parent of 0005569, not a child. Be advised that this wouldn't be just usefull for Unix.open_file. Other modules (extunix, lwt, ...) are using Unix.open_flags for syscalls that do accept O_CLOEXEC and would benefit from supporting a race-free CLOEXEC, too.

Issue History
Date Modified	Username	Field	Change
2012-03-30 23:44	goswin	New Issue
2012-04-01 00:28	doligez	Relationship added	child of 0005569
2012-04-01 00:30	doligez	Note Added: 0007256
2012-04-01 00:30	doligez	Status	new => feedback
2012-04-02 10:47	gerd	Note Added: 0007260
2012-04-03 15:18	xleroy	Relationship added	related to 0005256
2012-04-03 15:28	goswin	Note Added: 0007270
2012-04-03 15:28	goswin	Status	feedback => new
2012-04-10 17:40	doligez	Status	new => acknowledged
2012-07-09 17:42	doligez	Target Version	=> 4.01.0+dev
2012-07-31 13:36	doligez	Target Version	4.01.0+dev => 4.00.1+dev
2012-08-06 18:33	xleroy	Target Version	4.00.1+dev => 4.01.0+dev