balance command complains about missing rendezvous directory

[Marco Coletti]

I found a stray version of balance.exe outside of the cygwin direcotry tree.

Now the problem is this:
=======
$ /usr/sbin/balance -d -f -b 127.0.0.1 1080 127.0.0.1:1090
argv[0]=/usr/sbin/balance
bindhost=127.0.0.1
source port 1080
file /var/run/balance/balance.1080.127.0.0.1 already exists
using AF_UNSPEC
shmget: Function not implemented

$ cygcheck.exe /usr/sbin/balance
C:\cygwin64\usr\sbin\balance.exe
  C:\cygwin64\bin\cygwin1.dll
    C:\windows\system32\KERNEL32.dll
      C:\windows\system32\ntdll.dll
      C:\windows\system32\KERNELBASE.dll
========


Il giorno ven 14 giu 2019 alle ore 22:18 Brian Inglis
<Brian.Inglis@systematicsw.ab.ca> ha scritto:
>
> On 2019-06-14 09:25, Marco Coletti wrote:
> > Windows 10 x64
> > Just installed Cygwin and balance package.
> > =======
> > $ balance -d -f -b 127.0.0.1 1080 127.0.0.1:1090
> > source port 1080
> > ERROR: rendezvous directory not available and/or creatable
> >        please create /var/run/balance/ with mode 01777 like this:
> >        # mkdir -m 01777 /var/run/balance/
> > argv[0]=/usr/bin/balance
> > bindhost=127.0.0.1
> > $ ls -ld /var/run/balance
> > drwxrwxrwt+ 1 SO000419 Domain Users 0 Jun 14 16:48 /var/run/balance
> > $ ls -l /var/run/balance/.keep-balance
> > -rw-r--r-- 1 SO000419 Domain Users 0 Apr 28  2013 /var/run/balance/.keep-balance
> > ========
> > The same balance command works on Ubuntu 16.04.6.
>
> The error is produced by the following code in balance.c:
>
>   stat(SHMDIR, &buffer);
>   if (!S_ISDIR(buffer.st_mode)) {
>     mode_t old = umask(0);
>     if (mkdir(SHMDIR, 01777) < 0) {
>       if(errno != EEXIST) {
>         fprintf(stderr, "ERROR: rendezvous directory not available and/or
> creatable\n");
>         fprintf(stderr, "       please create %s with mode 01777 like this: \n",
> SHMDIR);
>         fprintf(stderr, "       # mkdir -m 01777 %s\n", SHMDIR);
>         umask(old);
>         exit(EX_UNAVAILABLE);
>       }
>     }
>     umask(old);
>   }
>
> where balance.h defines:
> #define SHMDIR          "/var/run/balance/"
>
> I ran mkdir under strace on a similar directory and got the expected errno:
> $ ls -dglo /var/run/blkid
> drwxrwxrwt+ 1 0 Mar 23 05:30 /var/run/blkid
> $ strace -o mkdir.strace /bin/mkdir -m01777 /var/run/blkid/
> /usr/bin/mkdir: cannot create directory ‘/var/run/blkid/’: File exists
> $ grep -m1 ', errno' mkdir.strace
> 58   71709 [main] mkdir 5564 mkdir: -1 = mkdir(/var/run/blkid, 1005), errno 17
> $ fgrep -w EEXIST /usr/include/sys/errno.h
> #define EEXIST 17       /* File exists */
>
> You could run balance under strace to see the errno reported:
> $ strace -o balance.strace balance -d -f -b 127.0.0.1 1080 127.0.0.1:1090
> and scan balance.strace log for the mkdir call and errno value as above, and
> what happens after.
>
> If the strace output does not show enough info, you may have to install the
> balance-debuginfo package to be able to run balance under gdb, to see the mkdir
> errno value returned, and what happens after.
>
> The quoted code is not very robust, as buffer is on the stack so starts with
> random bits, and the stat result is not checked to see if it succeeds, before
> checking the mode, which may be unset; it assumes static zero initialization,
> failing the mode check if stat fails; it would be safer rewritten as:
>
>   if (stat(SHMDIR, &buffer) < 0 ||
>       !S_ISDIR(buffer.st_mode)) {
>
> --
> Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
>
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> too much technical detail. Reader discretion is advised.
>
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