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Sometimes, depending on the bpf filter rules used in $PATTERN,

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the example script of the manpage feeds awk(1) with values larger
than UINT32_MAX.  Then awk prints a negative value, and this
messes up $BPFPROG.  Trying to load the resulting bpf byte codes
with ngctl then fails.

For example, the output for PATTERN="udp and dst net 255.255.0.0/16"
should be (all in one line):

    bpf_prog_len=10
    bpf_prog=[
      { code=40 jt=0 jf=0 k=12 }
      { code=21 jt=7 jf=0 k=34525 }
      { code=21 jt=0 jf=6 k=2048 }
      { code=48 jt=0 jf=0 k=23 }
      { code=21 jt=0 jf=4 k=17 }
      { code=32 jt=0 jf=0 k=30 }
      { code=84 jt=0 jf=0 k=4294901760 }
      { code=21 jt=0 jf=1 k=4294901760 }
      { code=6 jt=0 jf=0 k=8192 }
      { code=6 jt=0 jf=0 k=0 }
    ]

The two k=4294901760 values are displayed as k=-2147483648 by awk.

Replace the awk script of the manpage example with a slower but
safer version, that doesn't really attempt to convert the byte
code printed by tcpdump from string to number and back.

PR:		docs/123255
Submitted by:	Eugenio Maffione, eugenio.maffione at telecomitalia.it
MFC after:	3 days
This commit is contained in:
Giorgos Keramidas 2009-01-30 19:33:04 +00:00
parent 111a52201c
commit 7e7c1896a0
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=187935
1 changed files with 8 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
share/man/man4/ng_bpf.4
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@ -156,21 +156,14 @@ INHOOK="hook1"
MATCHHOOK="hook2"
NOTMATCHHOOK="hook3"
cat > /tmp/bpf.awk << xxENDxx
{
if (!init) {
printf "bpf_prog_len=%d bpf_prog=[", \\$1;
init=1;
} else {
printf " { code=%d jt=%d jf=%d k=%d }", \\$1, \\$2, \\$3, \\$4;
}
}
END {
print " ]"
}
xxENDxx
BPFPROG=`tcpdump -s 8192 -ddd ${PATTERN} | awk -f /tmp/bpf.awk`
BPFPROG=$( tcpdump -s 8192 -ddd ${PATTERN} | \\
( read len ; \\
echo -n "bpf_prog_len=$len" ; \\
echo -n "bpf_prog=[" ; \\
while read code jt jf k ; do \\
echo -n " { code=$code jt=$jt jf=$jf k=$k }" ; \\
done ; \\
echo " ]" ) )
ngctl msg ${NODEPATH} setprogram { thisHook=\\"${INHOOK}\\" \\
ifMatch=\\"${MATCHHOOK}\\" \\