netfilter buglog - Jan 2025 - [Bug 1786] New: ulogd_filter_HWHRD out of bounds array access in hwmac_str

https://bugzilla.netfilter.org/show_bug.cgi?id=1786

            Bug ID: 1786
           Summary: ulogd_filter_HWHRD out of bounds array access in
                    hwmac_str
           Product: ulogd
           Version: SVN (please provide timestamp)
          Hardware: x86_64
                OS: Ubuntu
            Status: NEW
          Severity: major
          Priority: P5
         Component: ulogd
          Assignee: netfilter-buglog at lists.netfilter.org
          Reporter: james at dingwall.me.uk

Created attachment 748
  --> https://bugzilla.netfilter.org/attachment.cgi?id=748&action=edit
increase size of hwmac_str array

This problem has already been addressed on the netfilter-devel:
https://lore.kernel.org/netfilter-devel/20250113123225.GC2068886 at
celephais.dreamlands/T/#m5c5518576fb781fe43db8680ec69f5379d7b5460

This report is being made to help investigate a bugzilla issue and does not
require any action (other than being closed as resolved)

This report relates to
https://bugs.launchpad.net/ubuntu/+source/ulogd2/+bug/2080677.

# apt-cache policy ulogd2
ulogd2:
  Installed: 2.0.8-2build1
  Candidate: 2.0.8-2build1
  Version table:
 *** 2.0.8-2build1 500
        500 http://gb.archive.ubuntu.com/ubuntu noble/universe amd64 Packages
        100 /var/lib/dpkg/status

# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 24.04.1 LTS
Release: 24.04
Codename: noble

It seems that there is an out of bounds array access in ulogd_filter_HWHDR.c
which leads to ulogd2 being terminated with SIGABRT and the following message
when it is compiled with -D_FORTIFY_SOURCE=3:

*** buffer overflow detected ***

The hwac_str array is defined as:

  static char hwmac_str[MAX_KEY - START_KEY][HWADDR_LENGTH];

Which translates to:

  static char hwmac_str[4 - 2][128];

i.e. an array of two elements, valid indexes 0, 1.

Adding a debug print statement in the parse_mac2str function:

  fprintf(stderr, "using hwmac_str index %d\n", okey - START_KEY);

will result in the following message:  

  using hwmac_str index 2

So the for loop attempts to format the mac address in to an invalid index in
hwmac_str.

As a simple test I made the definition of hwmac_str an array of 3 elements
which prevented the crash.  I don't know if it is correct to simply make
the array longer or if the bug is actually in the value of 'okey' passed
to
the function.  However based on the final return in interp_mac2str I think
the array definition is too short.  The attached patch allows ulog2 to
run after rebuilding with dpkg-buildpackage.

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