1. 09 Feb, 2017 2 commits
  2. 08 Feb, 2017 1 commit
  3. 07 Feb, 2017 1 commit
    • Stephen Smalley's avatar
      selinux: fix off-by-one in setprocattr · a050a570
      Stephen Smalley authored
      SELinux tries to support setting/clearing of /proc/pid/attr attributes
      from the shell by ignoring terminating newlines and treating an
      attribute value that begins with a NUL or newline as an attempt to
      clear the attribute.  However, the test for clearing attributes has
      always been wrong; it has an off-by-one error, and this could further
      lead to reading past the end of the allocated buffer since commit
      bb646cdb ("proc_pid_attr_write():
      switch to memdup_user()").  Fix the off-by-one error.
      
      Even with this fix, setting and clearing /proc/pid/attr attributes
      from the shell is not straightforward since the interface does not
      support multiple write() calls (so shells that write the value and
      newline separately will set and then immediately clear the attribute,
      requiring use of echo -n to set the attribute), whereas trying to use
      echo -n "" to clear the attribute causes the shell to skip the
      write() call altogether since POSIX says that a zero-length write
      causes no side effects. Thus, one must use echo -n to set and echo
      without -n to clear, as in the following example:
      $ echo -n unconfined_u:object_r:user_home_t:s0 > /proc/$$/attr/fscreate
      $ cat /proc/$$/attr/fscreate
      unconfined_u:object_r:user_home_t:s0
      $ echo "" > /proc/$$/attr/fscreate
      $ cat /proc/$$/attr/fscreate
      
      Note the use of /proc/$$ rather than /proc/self, as otherwise
      the cat command will read its own attribute value, not that of the shell.
      
      There are no users of this facility to my knowledge; possibly we
      should just get rid of it.
      
      UPDATE: Upon further investigation it appears that a local process
      with the process:setfscreate permission can cause a kernel panic as a
      result of this bug.  This patch fixes CVE-2017-2618.
      Signed-off-by: default avatarStephen Smalley <sds@tycho.nsa.gov>
      [PM: added the update about CVE-2017-2618 to the commit description]
      Cc: stable@vger.kernel.org # 3.5: d6ea83ecSigned-off-by: default avatarPaul Moore <paul@paul-moore.com>
      a050a570
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