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|
#!/bin/sh -eu
#
# SPDX-License-Identifier: AGPL-3.0-or-later
#
# PASST - Plug A Simple Socket Transport
# for qemu/UNIX domain socket mode
#
# PASTA - Pack A Subtle Tap Abstraction
# for network namespace/tap device mode
#
# seccomp.sh - Build seccomp profiles from "#syscalls[:PROFILE]" comments in code
#
# Copyright (c) 2021 Red Hat GmbH
# Author: Stefano Brivio <sbrivio@redhat.com>
TMP="$(mktemp)"
OUT="seccomp.h"
HEADER="/* This file was automatically generated by $(basename ${0}) */"
# Prefix for each profile: check that 'arch' in seccomp_data is matching
PRE='
struct sock_filter filter_@PROFILE@[] = {
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, arch))),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, PASST_AUDIT_ARCH, 0, @KILL@),
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, nr))),
'
# Suffix for each profile: return actions
POST=' BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL_PROCESS),
BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
};
'
# Syscall, @NR@: number, @ALLOW@: offset to RET_ALLOW, @NAME@: syscall name
CALL=' BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, @NR@, @ALLOW@, 0), /* @NAME@ */'
# Binary search tree node or leaf, @NR@: value, @R@: right jump, @L@: left jump
BST=' BPF_JUMP(BPF_JMP | BPF_JGE | BPF_K, @NR@, @R@, @L@),'
# sub() - Substitute in-place file line with processed template line
# $1: Line number
# $@: Replacement for @KEY@ in the form KEY:value
sub() {
IFS=
__line_no="${1}"
__template="$(eval printf '%s' "\${${2}}")"
shift; shift
sed -i "${__line_no}s#.*#${__template}#" "${TMP}"
for __def in ${@}; do
__key="@${__def%%:*}@"
__value="${__def#*:}"
sed -i "${__line_no}s/${__key}/${__value}/" "${TMP}"
done
unset IFS
}
# finish() - Finalise header file from temporary files with prefix and suffix
# $1: Variable name of prefix
# $@: Replacements for prefix variable
finish() {
IFS=
__out="$(eval printf '%s' "\${${1}}")"
shift
for __def in ${@}; do
__key="@${__def%%:*}@"
__value="${__def#*:}"
__out="$(printf '%s' "${__out}" | sed "s#${__key}#${__value}#")"
done
printf '%s\n' "${__out}" >> "${OUT}"
cat "${TMP}" >> "${OUT}"
rm "${TMP}"
printf '%s' "${POST}" >> "${OUT}"
unset IFS
}
# log2() - Binary logarithm
# $1: Operand
log2() {
__x=-1
__y=${1}
while [ ${__y} -gt 0 ]; do : $((__y >>= 1)); __x=$((__x + 1)); done
echo ${__x}
}
# gen_profile() - Build struct sock_filter for a single profile
# $1: Profile name
# $@: Names of allowed system calls, amount padded to next power of two
gen_profile() {
__profile="${1}"
shift
__statements_calls=${#}
__bst_levels=$(log2 $(( __statements_calls / 4 )) )
__statements_bst=$(( __statements_calls / 4 - 1 ))
__statements=$((__statements_calls + __statements_bst))
for __i in $(seq 1 ${__statements_bst} ); do
echo -1 >> "${TMP}"
done
for __i in $(seq 1 ${__statements_calls} ); do
ausyscall $(eval echo \${${__i}}) --exact >> "${TMP}"
done
sort -go "${TMP}" "${TMP}"
__distance=$(( __statements_calls / 2 ))
__level_nodes=1
__ll=0
__line=1
for __level in $(seq 1 $(( __bst_levels - 1 )) ); do
# Nodes
__cmp_pos=${__distance}
for __node in $(seq 1 ${__level_nodes}); do
__cmp_line=$(( __statements_bst + __cmp_pos ))
__lr=$(( __ll + 1 ))
__nr="$(sed -n ${__cmp_line}p "${TMP}")"
sub ${__line} BST "NR:${__nr}" "L:${__ll}" "R:${__lr}"
__ll=${__lr}
__line=$(( __line + 1 ))
__cmp_pos=$(( __cmp_pos + __distance * 2 ))
done
__distance=$(( __distance / 2 ))
__level_nodes=$(( __level_nodes * 2 ))
done
# Leaves
__ll=$(( __level_nodes - 1 ))
__lr=$(( __ll + __distance - 1 ))
__cmp_pos=${__distance}
for __leaf in $(seq 1 ${__level_nodes}); do
__cmp_line=$(( __statements_bst + __cmp_pos ))
__nr="$(sed -n ${__cmp_line}p "${TMP}")"
sub ${__line} BST "NR:${__nr}" "L:${__ll}" "R:${__lr}"
__ll=$(( __lr + __distance - 1 ))
__lr=$(( __ll + __distance))
__line=$(( __line + 1 ))
__cmp_pos=$(( __cmp_pos + __distance * 2 ))
done
# Calls
for __i in $(seq $(( __statements_bst + 1 )) ${__statements}); do
__nr="$(sed -n ${__i}p "${TMP}")"
__name=$(ausyscall ${__nr})
__allow=$(( __statements - __i + 1 ))
sub ${__i} CALL "NR:${__nr}" "NAME:${__name}" "ALLOW:${__allow}"
done
finish PRE "PROFILE:${__profile}" "KILL:$(( __statements + 1))"
}
printf '%s\n' "${HEADER}" > "${OUT}"
__profiles="$(sed -n 's/[\t ]*\*[\t ]*#syscalls:\([^ ]*\).*/\1/p' *.[ch] | sort -u)"
for __p in ${__profiles}; do
__calls="$(sed -n 's/[\t ]*\*[\t ]*#syscalls\(:'"${__p}"'\|\)[\t ]\{1,\}\(.*\)/\2/p' *.[ch] | tr ' ' '\n' | sort -u)"
echo "seccomp profile ${__p} allows: ${__calls}" | tr '\n' ' ' | fmt -t
# Pad here to keep gen_profile() "simple"
__count=0
for __c in ${__calls}; do __count=$(( __count + 1 )); done
__padded=$(( 1 << (( $(log2 ${__count}) + 1 )) ))
for __i in $( seq ${__count} $(( __padded - 1 )) ); do
__calls="${__calls} tuxcall"
done
gen_profile "${__p}" ${__calls}
done
|
