25. DHCP misses boundary check for network packet

Description:

The UEFI DHCP Protocol has many conventions for processing and caching incoming DHCP4/DHCP6 packets. Their current exists a check in PxeBcCacheDhcp4Packet before calling CopyMem() on two EFI_DHCP4_PACKET structs. This check uses an ASSERT which will be compiled out for RELEASE builds of UEFI on EDK II.

But actually, the source is from an external network, and there is no guarantee that the source Length is smaller than destination size. It might happen.

Recommendation:

  1. For this specific issue, we need remove ASSERT and use error checking.
  2. clarify the rule, ASSERT can only be used for something never happen. Error check must be used for something might happen.

This is addressed by EDK2 GIT
4f6b33b460226bc1a54d8af2c0f4fe195f2f04ce, 632dcfd6857b6211ce3fe9755d3c11e74ef5d4477, 471342bbefaac1c21fe7fa4e80949b552b12fbdd, a35dc6499beb0b76c340379a06dff74a8d38095a.

Acknowledgements:

Reported by Timzen, Topher topher.timzen@intel.com

References:

• USRT M1622

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