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Beniamino Galvani 0024cef238 n-dhcp4: fix BPF filter endianness issue 
The BPF filter takes the byte containing IP Flags and performs a
bitwise AND with "ntohs(IP_MF | IP_OFFMASK)".

On little-endian architectures the IP_MF flag (0x20) is ANDed with
0xFF3F and so the presence of the flag is correctly detected ignoring
other flags as IP_DF (0x40) or IP_RF (0x80).

On big-endian, "ntohs(IP_MF | IP_OFFMASK)" is 0x3FFF and so the filter
wrongly checks the presence of *any* flags. Therefore, a packet with
the DF flag set is dropped.

Instead, take the two bytes containing flags and offset:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version|  IHL  |Type of Service|          Total Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Identification        |Flags|      Fragment Offset    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

and verify that IP_MF and the offset are zero.

Fixes: e43b1791a3 ('Merge commit 'e23b3c9c3ac86b065eef002fa5c4321cc4a87df2' as 'shared/n-dhcp4'')

https://bugzilla.redhat.com/show_bug.cgi?id=1861488
https://github.com/nettools/n-dhcp4/pull/19
(cherry picked from commit 03d38e83e558802a82cb0e4847cb1f1ef75ccd16)
2020-08-04 16:10:02 +02:00
..
.github/workflows nettools: reimport nettools' n-dhcp4 and rework logging 2020-06-03 22:34:22 +02:00
src n-dhcp4: fix BPF filter endianness issue 2020-08-04 16:10:02 +02:00
subprojects nettools: reimport nettools' n-dhcp4 and rework logging 2020-06-03 22:34:22 +02:00
.editorconfig Merge commit 'e23b3c9c3ac86b065eef002fa5c4321cc4a87df2' as 'shared/n-dhcp4' 2019-05-25 02:02:04 +02:00
.gitmodules Merge commit 'e23b3c9c3ac86b065eef002fa5c4321cc4a87df2' as 'shared/n-dhcp4' 2019-05-25 02:02:04 +02:00
AUTHORS Merge commit 'e23b3c9c3ac86b065eef002fa5c4321cc4a87df2' as 'shared/n-dhcp4' 2019-05-25 02:02:04 +02:00
meson.build nettools: reimport nettools' n-dhcp4 and rework logging 2020-06-03 22:34:22 +02:00
NEWS.md Merge commit 'e23b3c9c3ac86b065eef002fa5c4321cc4a87df2' as 'shared/n-dhcp4' 2019-05-25 02:02:04 +02:00
README.md Merge commit 'e23b3c9c3ac86b065eef002fa5c4321cc4a87df2' as 'shared/n-dhcp4' 2019-05-25 02:02:04 +02:00

README.md

n-dhcp4

Dynamic Host Configuration Protocol for IPv4

The n-dhcp4 project implements the IPv4 Dynamic Host Configuration Protocol as defined in RFC-2132+.

Project

Requirements

The requirements for this project are:

  • Linux kernel >= 3.19
  • libc (e.g., glibc >= 2.16)

At build-time, the following software is required:

  • meson >= 0.41
  • pkg-config >= 0.29

Build

The meson build-system is used for this project. Contact upstream documentation for detailed help. In most situations the following commands are sufficient to build and install from source:

mkdir build
cd build
meson setup ..
ninja
meson test
ninja install

No custom configuration options are available.

Repository:

License:

  • Apache-2.0 OR LGPL-2.1-or-later
  • See AUTHORS file for details.