blog/Broken_umask_handling_with_sshfs.html

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   6     <title>Petter Reinholdtsen: Broken umask handling with sshfs</title>
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  12  <h1>
  13      <a href="http://people.skolelinux.org/pere/blog/">Petter Reinholdtsen</a>
  14
  15  </h1>
  16
  17 </div>
  18
  19
  20     <div class="entry">
  21       <div class="title">Broken umask handling with sshfs</div>
  22       <div class="date">26th August 2010</div>
  23       <div class="body"><p>My file system sematics program
  24 <a href="http://people.skolelinux.org/pere/blog/Testing_if_a_file_system_can_be_used_for_home_directories___.html">presented
  25 a few days ago</a> is very useful to verify that a file system can
  26 work as a unix home directory,and today I had to extend it a bit.  I'm
  27 looking into alternatives for home directory access here at the
  28 University of Oslo, and one of the options is sshfs.  My friend
  29 Finn-Arne mentioned a while back that they had used sshfs with Debian
  30 Edu, but stopped because of problems.  I asked today what the problems
  31 where, and he mentioned that sshfs failed to handle umask properly.
  32 Trying to detect the problem I wrote this addition to my fs testing
  33 script:</p>
  34
  35 <pre>
  36 mode_t touch_get_mode(const char *name, mode_t mode) {
  37   mode_t retval = 0;
  38   int fd = open(name, O_RDWR|O_CREAT|O_LARGEFILE, mode);
  39   if (-1 != fd) {
  40     unlink(name);
  41     struct stat statbuf;
  42     if (-1 != fstat(fd, &statbuf)) {
  43       retval = statbuf.st_mode & 0x1ff;
  44     }
  45     close(fd);
  46   }
  47   return retval;
  48 }
  49
  50 /* Try to detect problem discovered using sshfs */
  51 int test_umask(void) {
  52   printf("info: testing umask effect on file creation\n");
  53
  54   mode_t orig_umask = umask(000);
  55   mode_t newmode;
  56   if (0666 != (newmode = touch_get_mode("foobar", 0666))) {
  57     printf("  error: Wrong file mode %o when creating using mode 666 and umask 000\n",
  58            newmode);
  59   }
  60   umask(007);
  61   if (0660 != (newmode = touch_get_mode("foobar", 0666))) {
  62     printf("  error: Wrong file mode %o when creating using mode 666 and umask 007\n",
  63            newmode);
  64   }
  65
  66   umask (orig_umask);
  67   return 0;
  68 }
  69
  70 int main(int argc, char **argv) {
  71   [...]
  72   test_umask();
  73   return 0;
  74 }
  75 </pre>
  76
  77 <p>Sure enough.  On NFS to a netapp, I get this result:</p>
  78
  79 <pre>
  80 Testing POSIX/Unix sematics on file system
  81 info: testing symlink creation
  82 info: testing subdirectory creation
  83 info: testing fcntl locking
  84   Read-locking 1 byte from 1073741824
  85   Read-locking 510 byte from 1073741826
  86   Unlocking 1 byte from 1073741824
  87   Write-locking 1 byte from 1073741824
  88   Write-locking 510 byte from 1073741826
  89   Unlocking 2 byte from 1073741824
  90 info: testing umask effect on file creation
  91 </pre>
  92
  93 <p>When mounting the same directory using sshfs, I get this
  94 result:</p>
  95
  96 <pre>
  97 Testing POSIX/Unix sematics on file system
  98 info: testing symlink creation
  99 info: testing subdirectory creation
 100 info: testing fcntl locking
 101   Read-locking 1 byte from 1073741824
 102   Read-locking 510 byte from 1073741826
 103   Unlocking 1 byte from 1073741824
 104   Write-locking 1 byte from 1073741824
 105   Write-locking 510 byte from 1073741826
 106   Unlocking 2 byte from 1073741824
 107 info: testing umask effect on file creation
 108   error: Wrong file mode 644 when creating using mode 666 and umask 000
 109   error: Wrong file mode 640 when creating using mode 666 and umask 007
 110 </pre>
 111
 112 <p>So, I can conclude that sshfs is better than smb to a Netapp or a
 113 Windows server, but not good enough to be used as a home
 114 directory.</p>
 115
 116 <p>Update 2010-08-26: Reported the issue in
 117 <a href="http://bugs.debian.org/594498">BTS report #594498</a></p>
 118
 119 <p>Update 2010-08-27: Michael Gebetsroither report that he found the
 120 script so useful that he created a GIT repository and stored it in
 121 <a href="http://github.com/gebi/fs-test">http://github.com/gebi/fs-test</a>.</p>
 122 </div>
 123
 124       <div class="tags">Tags: <a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu</a>, <a href="http://people.skolelinux.org/pere/blog/tags/english">english</a>, <a href="http://people.skolelinux.org/pere/blog/tags/nuug">nuug</a>.</div>
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