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

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r@public.gmane.org]

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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