diff options
Diffstat (limited to 'net/apipa.sh')
| -rw-r--r-- | net/apipa.sh | 63 |
1 files changed, 29 insertions, 34 deletions
diff --git a/net/apipa.sh b/net/apipa.sh index 41274fa..a124b84 100644 --- a/net/apipa.sh +++ b/net/apipa.sh @@ -6,47 +6,42 @@ apipa_depend() program /sbin/arping /bin/arping } -_random_bytes_as_int() +_random_uint16() { - local hex num_bytes="$1" - - # While POSIX does not require that /dev/urandom exist, it is a - # de-facto standard. Therefore, the following approach should be - # highly portable in practice. In the case of Linux, and unlike BSD - # this interface does not block in the event that the CSRNG has not - # yet been seeded. Still, this is acceptable because we do not - # require a guarantee that the entropy be cryptographically secure. - # It's also worth noting that Linux >=5.4 is faster at seeding in - # the absence of RDRAND/RDSEED than previous versions were. + # While POSIX does not require that /dev/urandom exist, it is a de-facto + # standard. In the case of Linux, and unlike BSD, this interface does + # not block in the event that the CSRNG has not yet been seeded. + # Still, this is acceptable because we do not require a guarantee that + # the entropy be cryptographically secure. test -e /dev/urandom && - hex=$( - LC_ALL=C tr -dc '[:xdigit:]' < /dev/urandom | - dd bs="$(( num_bytes * 2 ))" count=1 2>/dev/null) && - test "${#hex}" = "$(( num_bytes * 2 ))" && - printf '%d\n' "0x${hex}" + printf %d 0x"$(LC_ALL=C od -vAn -N2 -tx1 /dev/urandom | tr -d '[:space:]')" } _random_apipa_octets() { local seed - # Obtain a highly random 16-bit seed for use by awk's RNG. In the - # unlikely event that the seed ends up being empty, awk will seed - # based on the time of day, with a granularity of one second. - seed=$(_random_bytes_as_int 2) + # Attempt to generate a random uint16 to seed awk's RNG. The maximum + # value of RAND_MAX known to be portable is 32767. Clamp accordingly by + # discarding one bit's worth of data. Should the seed turn out to be + # empty, we instruct awk to seed based on the time of day, in seconds. + seed=$(_random_uint16) && : $(( seed >>= 1 )) # For APIPA (RFC 3927), the 169.254.0.0/16 address block is # reserved. This provides 65024 addresses, having accounted for the # fact that the first and last /24 are reserved for future use. - awk "BEGIN { - srand($seed) - for (i=256; i<65280; i++) print rand() \" \" i - }" | - sort -k 1,1 -n | - POSIXLY_CORRECT=1 awk '{ - hex = sprintf("%04x",$2) - printf("%d %d\n", "0x" substr(hex,1,2), "0x" substr(hex,3,2)) - }' + awk -v seed="$seed" 'BEGIN { + if (seed != "") { + srand(seed) + } else { + srand() + } + for (i = 1; i < 255; i++) { + for (j = 0; j < 256; j++) { + printf("%f %d %d\n", rand(), i, j) + } + } + }' | sort -k 1,1 -n } apipa_start() @@ -62,11 +57,11 @@ apipa_start() addr=$( _random_apipa_octets | { - while read -r i1 i2; do - addr="169.254.${i1}.${i2}" - vebegin "${addr}/16" >&3 - if ! arping_address "${addr}" >&3; then - printf '%s\n' "${addr}" + while read -r f1 f2 f3; do + next_addr="169.254.$f2.$f3" + vebegin "$next_addr/16" >&3 + if ! arping_address "$next_addr" >&3; then + printf %s "$next_addr" exit 0 fi done |