libkmod: Use correct data types for ELF arithmetic

[stoeckmann]

Make sure that no input files could overflow internal variables used for calculations.

This prevents wrong output and out of boundary writes.

Proof of Concepts:

A: Wrong information printed

1. Create file with 4 billion mod versions

cat > poc.ko.zst.b64 << EOF
KLUv/WQQAG0DAEQEf0VMRgICABERIiIzMzMzRFUAQHd3d3eIiJmZqqoAQAADAAERAAAACCIzAAEA
C2ZmZmaZDF9fdmVyc2lvbnMAAHN5bQASIDCDqdQDAwDKhVvWG7ridkA+jvAfeuLGzgn1uytBMhyS
r3wKaAQjvcBa
EOF
base64 -d poc.ko.zst.b64 | zstd -d > poc.ko
dd if=/dev/zero of=poc.ko conv=notrunc bs=1 count=1 seek=274877907212

2. Print modversions (none will be shown)

modprobe --show-modversions poc.ko

B: Out of boundary write

1. Create file with 4 billion symbols

cat > poc.ko.zst.b64 << EOF
KLUv/WQUAG0DAJQEf0VMRgICABERIiIzMzMzRFUAQHd3d3eIiJmZqqoAQAADAAERAAAACCIzAAEA
EmZmZmaZFEBfX2tzeW10YWJfc3RyaW5ncwAAABEgcMOWOkDs3tArbgPk2wj/oRM1Fk4Iv7sSJMMQ
+eZTPCODyrcz
EOF
base64 -d poc.ko.zst.b64 | zstd -d > poc.ko
yes | tr '\n' '\0' | dd bs=4096 count=2097152 >> poc.ko

2. Print symbols (segmentation fault)

modprobe --show-exports poc.ko

[codecov]

Codecov Report

Attention: Patch coverage is 13.33333% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
libkmod/libkmod-elf.c	13.33%	12 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
libkmod/libkmod-elf.c	50.23% <13.33%> (ø)

[lucasdemarchi]

Applied, thanks.