[Bug 1747711] Re: file mis-identifies modern executables as application/x-sharedlib

[WHR]

>>> So for mime types to distinguish, "file" needs to grow reporting of
the INTERP presence.

Distinguish between shared libraries and PIC executables based on INTERP
ELF header is not always correct. Consider following 2 exceptions:

GLIBC main library libc-2.24.so
This shared object has an INTERP header, which is /lib64/ld-linux-x86-64.so.2 in my system. However we usually considering it a shared library, not an executable.

GLIBC dynamic linker ld-2.24.so
This shared object doesn't have INTERP header because this object itself is an interpreter. It should be considered as an executable since it is useful to load and run GLIBC linked dynamic executables.

This indicates a clear boundary between shared libraries and PIC
executables just does not exist.

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Title:
  file mis-identifies modern executables as application/x-sharedlib

Status in file package in Ubuntu:
  Confirmed

Bug description:
  file doesn't recognize modern PIE (Position Independent Executable)
  x86 executables as such, reporting them as “application/x-sharedlib”.
  Consequently, only non-PIE executables can be opened in graphical file
  managers such as nautilus. This may cause a minor (?) security risk if
  a commonly-published workaround is attempted.

  Expected behaviour:

      $ echo "int main() { return 0; }" > foo.c
      $ gcc -o foo foo.c
      $ file foo
      foo: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=6e7749f995a89a53f74ec29d3c16fcf3f56be90f, not stripped
      $ file --mime-type foo
      foo: application/x-executable

  Actual behaviour:

      $ echo "int main() { return 0; }" > foo.c
      $ gcc -o foo foo.c
      $ file foo
      foo: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=6e7749f995a89a53f74ec29d3c16fcf3f56be90f, not stripped
      $ file --mime-type foo
      foo: application/x-sharedlib

  Workaround (unsafe?):

      $ echo "int main() { return 0; }" > foo.c
      $ gcc -o foo-nopie foo.c -no-pie
      $ file foo-nopie
      foo-nopie: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=3eb8c581f43c19997e3c828f5a9730dbdc794470, not stripped
      $ file --mime-type foo-nopie
      foo-nopie: application/x-executable

  gcc now defaults to building with PIE enabled for security reasons.

  Also affects: nautilus (and likely other graphical file managers like
  those on Lubuntu) - because nautilus uses mime-type to determine if a
  file is executable, double-click to run a program no longer works.

  Also noted on: Gnome Bugs -
  https://bugzilla.gnome.org/show_bug.cgi?id=737849 (2014) - before PIE
  became the default build option.

  This may be an upstream issue. This may not affect architectures
  outside x86.*

  ProblemType: Bug
  DistroRelease: Ubuntu 17.10
  Package: file 1:5.32-1
  ProcVersionSignature: Ubuntu 4.13.0-32.35-generic 4.13.13
  Uname: Linux 4.13.0-32-generic x86_64
  ApportVersion: 2.20.7-0ubuntu3.7
  Architecture: amd64
  CurrentDesktop: GNOME
  Date: Tue Feb  6 11:21:20 2018
  InstallationDate: Installed on 2017-05-11 (270 days ago)
  InstallationMedia: Ubuntu-GNOME 17.04 "Zesty Zapus" - Release amd64 (20170412)
  SourcePackage: file
  UpgradeStatus: Upgraded to artful on 2017-10-21 (108 days ago)

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