1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
|
[[!meta copyright="Copyright © 2012 Free Software Foundation, Inc."]]
[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
id="license" text="Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
is included in the section entitled [[GNU Free Documentation
License|/fdl]]."]]"""]]
[[!meta title="O_EXEC"]]
[[!tag open_issue_glibc open_issue_hurd]]
# IRC, freenode, #hurd, 2012-04-24
<pinotree> interesting, glibc on every OS except hurd (so including linux
too) does not define O_EXEC
<pinotree> can somebody please help me understand a POSIX behaviour?
<pinotree> it's about fexecve:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/fexecve.html
<pinotree> basically, it seems to me (reading the "errors" and "application
usage" sections) that O_EXEC for open() the fd is not mandatory, and if
not used fexecve will check for file permission at call time?
<pinotree> because currently libdiskfs and libnetfs require the fd to be
open with O_EXEC
<braunr> "Since execute permission is checked by fexecve(), the file
description fd need not have been opened with the O_EXEC flag"
<braunr> this one makes it clear checking for O_EXEC is wrong
<braunr> it looks like O_EXEC is only needed when you want to have files
for which only the execution permission is set
<braunr> but not the read one
<braunr> (i don't understand the "and write" part though)
<braunr> "exec will fail if the mode of the file associated with fd does
not grant execute permission to the calling process at the time fexecve()
is called."
<braunr> this one strengthens the impression you have, that fexecve indeed
checks file permissions at the time it's called
<braunr> pinotree: hope it helps
<pinotree> so it implies the following:
<pinotree> O_RDONLY → exec works if the file is readable
<braunr> exec works if the file is readable and/or executable (although
without read permissions you can't check it)
<braunr> (well, fexecve)
<pinotree> O_EXEC → exec requires that the permission of the file at
fexecve() time have +x
<braunr> i'd say ye so far
<braunr> yes
<pinotree> so we need to fix lib{disk,net}fs then
<braunr> seems so
<pinotree> enlighting, merci braunr
<braunr> de rien
<pinotree> :)
|
