0000331: Add 'x' mode to fopen and freopen to force O_EXCL (and declare that fdopen ignores 'x')

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Category

Severity

Type

Date Submitted

Last Update

0000331

[1003.1(2008)/Issue 7] System Interfaces

Objection

Enhancement Request

2010-10-11 22:23

2011-09-22 16:25

Reporter

dwheeler

View Status

public

Assigned To

ajosey

Priority

normal

Resolution

Duplicate

Status

Closed

Name

David A. Wheeler

Organization

User Reference

Section

XSH - fopen, freopen, and fdopen

Page Number

820-926

Line Number

27373-31021

Interp Status

---

Final Accepted Text

Summary

0000331: Add 'x' mode to fopen and freopen to force O_EXCL (and declare that fdopen ignores 'x')

Description

Some security vulnerabilities can be countered by exclusively opening a file using, e.g., open's O_EXCL flag (e.g., see the discussion on CWE-377, Insecure Temporary File). Unfortunately, fopen and freopen don't provide a standard flag for accessing this. Making it easier to invoke this would make it easier to avoid certain security vulnerabilities.

GNU/Linux *does* provide such a flag, 'x', for fopen and freopen.
This proposal recommends making it a standard flag. Per its man page,
the flag 'x' in a mode has this meaning:
       x Open the file exclusively (like the O_EXCL flag of open(2)). If
              the file already exists, fopen() fails, and sets errno to EEX-
              IST. This flag is ignored for fdopen().

Desired Action

In fopen, after line 29134:
If the flag 'x' is included in the mode and after the first character, open the file exclusively, just as if including the O_EXCL | O_CREAT flags of open(2).
If the file already exists, fail and set errno to EEXIST.

In freopen, after line 30889:
If the flag 'x' is included in the mode and after the first character,
attempt to open the file exclusively,
just as if including the O_EXCL | O_CREAT flags of open(2).
If the file already exists, fail and set errno to EEXIST.

In fdopen, after line 27388:
If the flag 'x' is included in the mode, it is ignored.

Tags

c99

Attached Files

Relationships

duplicate of

0000411

Applied

ajosey

adding atomic FD_CLOEXEC support

Notes
(0000592) nick (manager) 2010-10-28 16:14	Please note that the C committee is considering a similar change (they require that the 'x' character be the last character in the mode string). We should wait till that standard is complete and align with their change. For a current working draft of the C revision, see http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1516.pdf [^]

(0000610) nick (manager) 2010-11-05 15:11	The committee draft ballot for the C1x standard is due to start within the next 2-3 weeks. The 'x' character for fopen is regarded as non-controversial.

(0000972) nick (manager) 2011-09-22 16:23 edited on: 2011-09-22 16:24	Closing as duplicate of 0000411

Issue History
Date Modified	Username	Field	Change
2010-10-11 22:23	dwheeler	New Issue
2010-10-11 22:23	dwheeler	Status	New => Under Review
2010-10-11 22:23	dwheeler	Assigned To	=> ajosey
2010-10-11 22:23	dwheeler	Name	=> David A. Wheeler
2010-10-11 22:23	dwheeler	Section	=> XSH - fopen, freopen, and fdopen
2010-10-11 22:23	dwheeler	Page Number	=> 820-926
2010-10-11 22:23	dwheeler	Line Number	=> 27373-31021
2010-10-28 16:12	nick	Tag Attached: c99
2010-10-28 16:14	nick	Note Added: 0000592
2010-11-05 15:11	nick	Note Added: 0000610
2011-09-22 16:21	eblake	Relationship added	related to 0000411
2011-09-22 16:22	nick	Relationship replaced	duplicate of 0000411
2011-09-22 16:23	nick	Interp Status	=> ---
2011-09-22 16:23	nick	Note Added: 0000972
2011-09-22 16:23	nick	Status	Under Review => Resolved
2011-09-22 16:23	nick	Resolution	Open => Duplicate
2011-09-22 16:24	nick	Note Edited: 0000972
2011-09-22 16:25	nick	Status	Resolved => Closed

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