netdev - Re: [PATCH iproute2 v2] utils: don't match empty strings as prefixes

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Message-ID: <20190715134956.1e7af534@hermes.lan>
Date:   Mon, 15 Jul 2019 13:49:56 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Matteo Croce <mcroce@...hat.com>
Cc:     netdev@...r.kernel.org, David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH iproute2 v2] utils: don't match empty strings as
 prefixes

On Mon, 15 Jul 2019 20:04:30 +0200
Matteo Croce <mcroce@...hat.com> wrote:

> iproute has an utility function which checks if a string is a prefix for
> another one, to allow use of abbreviated commands, e.g. 'addr' or 'a'
> instead of 'address'.
> 
> This routine unfortunately considers an empty string as prefix
> of any pattern, leading to undefined behaviour when an empty
> argument is passed to ip:
> 
>     # ip ''
>     1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
>         link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>         inet 127.0.0.1/8 scope host lo
>            valid_lft forever preferred_lft forever
>         inet6 ::1/128 scope host
>            valid_lft forever preferred_lft forever
> 
>     # tc ''
>     qdisc noqueue 0: dev lo root refcnt 2
> 
>     # ip address add 192.0.2.0/24 '' 198.51.100.1 dev dummy0
>     # ip addr show dev dummy0
>     6: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 1000
>         link/ether 02:9d:5e:e9:3f:c0 brd ff:ff:ff:ff:ff:ff
>         inet 192.0.2.0/24 brd 198.51.100.1 scope global dummy0
>            valid_lft forever preferred_lft forever
> 
> Rewrite matches() so it takes care of an empty input, and doesn't
> scan the input strings three times: the actual implementation
> does 2 strlen and a memcpy to accomplish the same task.
> 
> Signed-off-by: Matteo Croce <mcroce@...hat.com>

Thanks for following up. Applied