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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  14  <h1>
  15      <a href="http://people.skolelinux.org/pere/blog/">Petter Reinholdtsen</a>
  16
  17  </h1>
  18
  19 </div>
  20
  21
  22     <div class="entry">
  23       <div class="title">Broken umask handling with sshfs</div>
  24       <div class="date">26th August 2010</div>
  25       <div class="body"><p>My file system sematics program
  26 <a href="http://people.skolelinux.org/pere/blog/Testing_if_a_file_system_can_be_used_for_home_directories___.html">presented
  27 a few days ago</a> is very useful to verify that a file system can
  28 work as a unix home directory,and today I had to extend it a bit.  I'm
  29 looking into alternatives for home directory access here at the
  30 University of Oslo, and one of the options is sshfs.  My friend
  31 Finn-Arne mentioned a while back that they had used sshfs with Debian
  32 Edu, but stopped because of problems.  I asked today what the problems
  33 where, and he mentioned that sshfs failed to handle umask properly.
  34 Trying to detect the problem I wrote this addition to my fs testing
  35 script:</p>
  36
  37 <pre>
  38 mode_t touch_get_mode(const char *name, mode_t mode) {
  39   mode_t retval = 0;
  40   int fd = open(name, O_RDWR|O_CREAT|O_LARGEFILE, mode);
  41   if (-1 != fd) {
  42     unlink(name);
  43     struct stat statbuf;
  44     if (-1 != fstat(fd, &statbuf)) {
  45       retval = statbuf.st_mode & 0x1ff;
  46     }
  47     close(fd);
  48   }
  49   return retval;
  50 }
  51
  52 /* Try to detect problem discovered using sshfs */
  53 int test_umask(void) {
  54   printf("info: testing umask effect on file creation\n");
  55
  56   mode_t orig_umask = umask(000);
  57   mode_t newmode;
  58   if (0666 != (newmode = touch_get_mode("foobar", 0666))) {
  59     printf("  error: Wrong file mode %o when creating using mode 666 and umask 000\n",
  60            newmode);
  61   }
  62   umask(007);
  63   if (0660 != (newmode = touch_get_mode("foobar", 0666))) {
  64     printf("  error: Wrong file mode %o when creating using mode 666 and umask 007\n",
  65            newmode);
  66   }
  67
  68   umask (orig_umask);
  69   return 0;
  70 }
  71
  72 int main(int argc, char **argv) {
  73   [...]
  74   test_umask();
  75   return 0;
  76 }
  77 </pre>
  78
  79 <p>Sure enough.  On NFS to a netapp, I get this result:</p>
  80
  81 <pre>
  82 Testing POSIX/Unix sematics on file system
  83 info: testing symlink creation
  84 info: testing subdirectory creation
  85 info: testing fcntl locking
  86   Read-locking 1 byte from 1073741824
  87   Read-locking 510 byte from 1073741826
  88   Unlocking 1 byte from 1073741824
  89   Write-locking 1 byte from 1073741824
  90   Write-locking 510 byte from 1073741826
  91   Unlocking 2 byte from 1073741824
  92 info: testing umask effect on file creation
  93 </pre>
  94
  95 <p>When mounting the same directory using sshfs, I get this
  96 result:</p>
  97
  98 <pre>
  99 Testing POSIX/Unix sematics on file system
 100 info: testing symlink creation
 101 info: testing subdirectory creation
 102 info: testing fcntl locking
 103   Read-locking 1 byte from 1073741824
 104   Read-locking 510 byte from 1073741826
 105   Unlocking 1 byte from 1073741824
 106   Write-locking 1 byte from 1073741824
 107   Write-locking 510 byte from 1073741826
 108   Unlocking 2 byte from 1073741824
 109 info: testing umask effect on file creation
 110   error: Wrong file mode 644 when creating using mode 666 and umask 000
 111   error: Wrong file mode 640 when creating using mode 666 and umask 007
 112 </pre>
 113
 114 <p>So, I can conclude that sshfs is better than smb to a Netapp or a
 115 Windows server, but not good enough to be used as a home
 116 directory.</p>
 117
 118 <p>Update 2010-08-26: Reported the issue in
 119 <a href="http://bugs.debian.org/594498">BTS report #594498</a></p>
 120
 121 <p>Update 2010-08-27: Michael Gebetsroither report that he found the
 122 script so useful that he created a GIT repository and stored it in
 123 <a href="http://github.com/gebi/fs-test">http://github.com/gebi/fs-test</a>.</p>
 124 </div>
 125
 126       <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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