patches/squashfs-tools/0014-also-set-stickybit-as-non-root.patch

   1 Subject: [PATCH 0/2] Preserve the sticky bit
   2
   3 The unsquashfs tool was masking off the sticky bit when running as a
   4 non-root user. It isn't documented why the bit was being masked off but
   5 there are at least two possibilities.
   6
   7 The first is because all of the files created by unsquashfs, when
   8 running as a non-root user, will be owned by the same user since
   9 unsquashfs can't chown() the files.I think it is still good practice to
  10 attempt to preserve the sticky bit in this situation because it is
  11 perfectly valid to have a world-writable directory containing files
  12 owned by a single user. The sticky bit set on the directory inode would
  13 prevent other users from deleting those files.
  14
  15 Another reason why the sticky bit was being masked off when running as
  16 non-root could be due to this snippet from the chmod(2) man page:
  17
  18   On some filesystems, only the superuser can set the sticky bit, which
  19   may have a special meaning. For the sticky bit, and for set-user-ID
  20   and set-group-ID bits on directories, see stat(2).
  21
  22 However, I'm not seeing any Linux filesystems that require root
  23 privileges in order to set the sticky bit after a quick search through
  24 v4.17. In the case that such filesystems do exist, old behavior is
  25 preserved by retrying a failed chmod() without the sticky bit.
  26
  27 Setting the sticky bit, when non-root, will not cause any problems in
  28 unsquashfs because all of the created files will by owned by the same
  29 user. Therefore, unsquashfs will not run into any of the restricted
  30 deletion protections after setting the sticky bit on a directory inode
  31 even if unsquashfs needs to remove or rename a file underneath the
  32 directory.
  33
  34 Signed-off-by: Tyler Hicks <tyhicks@...>
  35 ---
  36  squashfs-tools/unsquashfs.c | 17 +++++++++++++----
  37  1 file changed, 13 insertions(+), 4 deletions(-)
  38
  39 Origin: https://sourceforge.net/p/squashfs/mailman/message/36343213/
  40 Forwarded: yes
  41 Bug-Ubuntu: https://launchpad.net/bugs/1779914
  42
  43 Index: squashfs-tools-4.3/squashfs-tools/unsquashfs.c
  44 ===================================================================
  45 --- squashfs-tools-4.3.orig/squashfs-tools/unsquashfs.c
  46 +++ squashfs-tools-4.3/squashfs-tools/unsquashfs.c
  47 @@ -822,7 +822,7 @@ int set_attributes(char *pathname, int m
  48  {
  49         struct utimbuf times = { time, time };
  50         /* Mode bits that are only useful with root privileges */
  51 -       mode_t root_mask = S_ISUID | S_ISGID | S_ISVTX;
  52 +       mode_t root_mask = S_ISUID | S_ISGID;
  53
  54         if(utime(pathname, &times) == -1) {
  55                 ERROR("set_attributes: failed to set time on %s, because %s\n",
  56 @@ -841,9 +841,18 @@ int set_attributes(char *pathname, int m
  57                 mode &= ~(root_mask);
  58
  59         if((set_mode || (mode & root_mask)) && chmod(pathname, (mode_t) mode) == -1) {
  60 -               ERROR("set_attributes: failed to change mode %s, because %s\n",
  61 -                       pathname, strerror(errno));
  62 -               return FALSE;
  63 +               /*
  64 +                * Some filesystems require root privileges to use the sticky
  65 +                * bit. If we're not root and chmod() failed with EPERM when the
  66 +                * sticky bit was included in the mode, try again without the
  67 +                * sticky bit. Otherwise, fail with an error message.
  68 +                */
  69 +               if (root_process || errno != EPERM || !(mode & S_ISVTX) ||
  70 +                               chmod(pathname, (mode_t) (mode & ~S_ISVTX)) == -1) {
  71 +                       ERROR("set_attributes: failed to change mode %s, because %s\n",
  72 +                               pathname, strerror(errno));
  73 +                       return FALSE;
  74 +               }
  75         }
  76
  77         write_xattr(pathname, xattr);