[Bug 71061] New: msgctl(2) manpage : put back a condition of EPERM error code forgotten

[Bug 71061] New: msgctl(2) manpage : put back a condition of EPERM error code forgotten

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=71061

            Bug ID: 71061
           Summary: msgctl(2) manpage : put back a condition of EPERM
                    error code forgotten
           Product: Documentation
           Version: unspecified
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: man-pages
          Assignee: documentation_man-pages-ztI5WcYan/vQLgFONoPN62D2FQJk+8+b@public.gmane.org
          Reporter: fboiteux-N+jn5RlININWk0Htik3J/w@public.gmane.org
        Regression: No

Hello,

  I've noticed in the msgctl(2) manpage that a condition to get an EPERM error
code was dropped in the past : it's about trying to modify the size of a
message queue (msg_qbytes) larger than the max size set in kernel (look at
/proc/sys/kernel/msgmnb).

In a (very old) manpage of a Debian Woody 3.0 (!), we could read :

       EPERM      The argument cmd has value IPC_SET or IPC_RMID but the
calling process effective user-ID has insufficient privileges to
                  execute  the  command.   Note this is also the case of a non
super-user process trying to increase the msg_qbytes value
                  beyond the value specified by the system parameter MSGMNB.


thereas on later pages (on my Debian Wheezy 7.4, but also in current version of
kernel manpages), we only have :

       EPERM  The argument cmd has the value IPC_SET or IPC_RMID, but the
effective user ID of the calling process is not the creator  (as  found  in
              msg_perm.cuid) or the owner (as found in msg_perm.uid) of the
message queue, and the process is not privileged (Linux: it does not have
              the CAP_SYS_ADMIN capability).


Could you put back in the man page a sentence like : 'Note this is also the
case of a non super-user process trying to increase the msg_qbytes value
                  beyond the value specified by the system parameter MSGMNB.'


      Thanks,
            Frédéric.

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[Bug 71061] msgctl(2) manpage : put back a condition of EPERM error code forgotten

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=71061

Frédéric Boiteux <fboiteux-N+jn5RlININWk0Htik3J/w@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fboiteux-N+jn5RlININWk0Htik3J/w@public.gmane.org
         Regression|No                          |Yes

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[Bug 71061] msgctl(2) manpage : put back a condition of EPERM error code forgotten

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=71061

Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
         Resolution|---                         |CODE_FIX

--- Comment #1 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
(In reply to Frédéric Boiteux from comment #0)
> Hello,
> 
>   I've noticed in the msgctl(2) manpage that a condition to get an EPERM
> error code was dropped in the past : it's about trying to modify the size of
> a message queue (msg_qbytes) larger than the max size set in kernel (look at
> /proc/sys/kernel/msgmnb).
> 
> In a (very old) manpage of a Debian Woody 3.0 (!), we could read :
> 
>        EPERM      The argument cmd has value IPC_SET or IPC_RMID but the
> calling process effective user-ID has insufficient privileges to
>                   execute  the  command.   Note this is also the case of a
> non super-user process trying to increase the msg_qbytes value
>                   beyond the value specified by the system parameter MSGMNB.
> 
> 
> thereas on later pages (on my Debian Wheezy 7.4, but also in current version
> of kernel manpages), we only have :
> 
>        EPERM  The argument cmd has the value IPC_SET or IPC_RMID, but the
> effective user ID of the calling process is not the creator  (as  found  in
>               msg_perm.cuid) or the owner (as found in msg_perm.uid) of the
> message queue, and the process is not privileged (Linux: it does not have
>               the CAP_SYS_ADMIN capability).
> 
> 
> Could you put back in the man page a sentence like : 'Note this is also the
> case of a non super-user process trying to increase the msg_qbytes value
>                   beyond the value specified by the system parameter MSGMNB.'
> 

Yes, it is puzzling that that text was dropped. It was done back in 1.51,
before the days of version control or mailing lists for man-pages, so I can't
divine the reason. Nevertheless, elsewhere in the page, it notes that a
capability is required to raise this value above MSGMNB. (And there was a typo
in that text, where it mentioned CAP_IPC_RESOURCE; should be CAP_SYS_RESOURCE;
fixed now). So, obviously, a fix is required. I applied the patch below. Thanks
for your report.

diff --git a/man2/msgctl.2 b/man2/msgctl.2
index e092fcb..ea39e10 100644
--- a/man2/msgctl.2
+++ b/man2/msgctl.2
@@ -311,6 +311,17 @@ of the message queue,
 and the process is not privileged (Linux: it does not have the
 .B CAP_SYS_ADMIN
 capability).
+.TP
+.B EPERM
+An attempt
+.RB ( IPC_SET )
+was made to increase
+.I msg_qbytes
+beyond the system parameter
+.BR MSGMNB ,
+but the caller is not privileged (Linux: does not have the
+.B CAP_SYS_RESOURCE
+capability).
 .SH CONFORMING TO
 SVr4, POSIX.1-2001.
 .\" SVID does not document the EIDRM error condition.

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