The ice_get_pfa_module_tlv() function iterates over the Type-Length-Value
structures in the Preserved Fields Area (PFA) of the NVM. This is used by
the driver to access data such as the Part Board Assembly identifier.

The function uses simple logic to iterate over the PFA. First, the pointer
to the PFA in the NVM is read. Then the total length of the PFA is read
from the first word.

A pointer to the first TLV is initialized, and a simple loop iterates over
each TLV. The pointer is moved forward through the NVM until it exceeds the
PFA area.

The logic seems sound, but it is missing a key detail. The Preserved
Fields Area length includes one additional final word. This is documented
in the device data sheet as a dummy word which contains 0xFFFF. All NVMs
have this extra word.

If the driver tries to scan for a TLV that is not in the PFA, it will read
past the size of the PFA. It reads and interprets the last dummy word of
the PFA as a TLV with type 0xFFFF. It then reads the word following the PFA
as a length.

The PFA resides within the Shadow RAM portion of the NVM, which is
relatively small. All of its offsets are within a 16-bit size. The PFA
pointer and TLV pointer are stored by the driver as 16-bit values.

In almost all cases, the word following the PFA will be such that
interpreting it as a length will result in 16-bit arithmetic overflow. Once
overflowed, the new next_tlv value is now below the maximum offset of the
PFA. Thus, the driver will continue to iterate the data as TLVs. In the
worst case, the driver hits on a sequence of reads which loop back to
reading the same offsets in an endless loop.

To fix this, we need to correct the loop iteration check to account for
this extra word at the end of the PFA. This alone is sufficient to resolve
the known cases of this issue in the field. However, it is plausible that
an NVM could be misconfigured or have corrupt data which results in the
same kind of overflow. Protect against this by using check_add_overflow
when calculating both the maximum offset of the TLVs, and when calculating
the next_tlv offset at the end of each loop iteration. This ensures that
the driver will not get stuck in an infinite loop when scanning the PFA.

Fixes: e961b679 ("ice: add board identifier info to devlink .info_get")
Co-developed-by: Paul Greenwalt <paul.greenwalt@intel.com>
Signed-off-by: Paul Greenwalt <paul.greenwalt@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20240603-net-2024-05-30-intel-net-fixes-v2-1-e3563aa89b0c@intel.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>