[PATCH iproute2] routel: fix infinite loop in line parser

[PATCH iproute2] routel: fix infinite loop in line parser

[Michal Kubecek]

As noticed by one of the few users of routel script, it ends up in an
infinite loop when they pull out the cable from the NIC used for some
route. This is caused by its parser expecting the line of "ip route show"
output consists of "key value" pairs (except for the initial target range),
together with an old trap of Bourne style shells that "shift 2" does
nothing if there is only one argument left. Some keywords, e.g. "linkdown",
are not followed by a value.

Improve the parser to

  (1) only set variables for keywords we care about
  (2) recognize (currently) known keywords without value

This is still far from perfect (and certainly not future proof) but to
fully fix the script, one would probably have to rewrite the logic
completely (and I'm not sure it's worth the effort).

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
---
 ip/routel | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/ip/routel b/ip/routel
index 8d1d352abdff..9a30462aa6b2 100644
--- a/ip/routel
+++ b/ip/routel
@@ -32,10 +32,22 @@ ip route list table "$@" |
     esac
     while test $# != 0
     do
-       key=$1
-       val=$2
-       eval "$key=$val"
-       shift 2
+       case "$1" in
+          proto|via|dev|scope|src|table)
+             key=$1
+             val=$2
+             eval "$key='$val'"
+             shift 2
+             ;;
+          dead|onlink|pervasive|offload|notify|linkdown|unresolved)
+             shift
+             ;;
+          *)
+             # avoid infinite loop on unknown keyword without value at line end
+             shift
+             shift
+             ;;
+       esac
     done
     echo "$network	$via	$src	$proto	$scope	$dev	$table"
  done | awk -F '	' '
-- 
2.12.2

Re: [PATCH iproute2] routel: fix infinite loop in line parser

[Stephen Hemminger]

On Thu, 27 Apr 2017 11:43:47 +0200 (CEST)
Michal Kubecek <mkubecek@suse.cz> wrote:

> As noticed by one of the few users of routel script, it ends up in an
> infinite loop when they pull out the cable from the NIC used for some
> route. This is caused by its parser expecting the line of "ip route show"
> output consists of "key value" pairs (except for the initial target range),
> together with an old trap of Bourne style shells that "shift 2" does
> nothing if there is only one argument left. Some keywords, e.g. "linkdown",
> are not followed by a value.
> 
> Improve the parser to
> 
>   (1) only set variables for keywords we care about
>   (2) recognize (currently) known keywords without value
> 
> This is still far from perfect (and certainly not future proof) but to
> fully fix the script, one would probably have to rewrite the logic
> completely (and I'm not sure it's worth the effort).
> 
> Signed-off-by: Michal Kubecek <mkubecek@suse.cz>

Appled, but this really needs to be done better.
Either as a simplified output of route command. See ip -br link
Or ip route should have a json output option and use python/perl/xss
to reformat.

Re: [PATCH iproute2] routel: fix infinite loop in line parser

[Michal Kubecek]

On Thu, Apr 27, 2017 at 04:46:47PM -0700, Stephen Hemminger wrote:
> 
> Appled, but this really needs to be done better.
> Either as a simplified output of route command. See ip -br link
> Or ip route should have a json output option and use python/perl/xss
> to reformat.

Agreed, parsing the output of ip command is certainly not the right way.

I must admit that I had no idea this script exists until the bug report
landed on my table (and I had to use "rpm -qf" to learn that it's part
of iproute2 package). And I suspect I may not be the only one.

Michal Kubecek