[Bug 1810241] Re: NULL dereference when decompressing specially crafted archives

[Jeffrey Hawkins]

This issue is shown as Open on Jammy.  The CVE is applicable to 1.32 and
prior versions of TAR.  Jammy uses 1.34, so this status should be not
affected or closed.  This was fixed in Focal in
1.30+dfsg-7ubuntu0.20.04.1.  Please update the CVE status on Jammy.

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Title:
  NULL dereference when decompressing specially crafted archives

Status in tar package in Ubuntu:
  Triaged

Bug description:
  Hi,

  Fuzzing tar with checksums disabled reveals a NULL pointer dereference
  when parsing certain archives that have malformed extended headers.
  This affects tar from (at least) Trusty, Bionic and Cosmic. I haven't
  tested Xenial's version.

  A test case with fixed checksums is attached. To avoid breaking
  anything that looks inside tar archives, I have converted it to text
  with xxd. To reproduce:

  $ xxd -r gnutar-crash.tar.txt gnutar-crash.tar
  $ tar Oxf gnutar-crash.tar 
  tar: Ignoring unknown extended header keyword 'GNU.sparse.minTr'
  tar: Malformed extended header: missing length
  Segmentation fault (core dumped)

  I have also attached a patch against the latest upstream git and
  against 1.30 (in Cosmic). This fixes the issue by detecting the null
  result before it is dereferenced.

  Regards,
  Daniel

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