Re: [PATCH] drivers/net/wan/hdlc_ppp: fix potential null pointer in ppp_cp_event logging

["Krzysztof Hałasa" <khalasa@piap.pl>]

Hi Kriish,

Kriish Sharma <kriish.sharma2006@gmail.com> writes:

> Fixes warnings observed during compilation with -Wformat-overflow:
>
> drivers/net/wan/hdlc_ppp.c: In function ‘ppp_cp_event’:
> drivers/net/wan/hdlc_ppp.c:353:17: warning: ‘%s’ directive argument is null [-Wformat-overflow=]
>   353 |                 netdev_info(dev, "%s down\n", proto_name(pid));
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/net/wan/hdlc_ppp.c:342:17: warning: ‘%s’ directive argument is null [-Wformat-overflow=]
>   342 |                 netdev_info(dev, "%s up\n", proto_name(pid));
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It appears proto_name(pid) never returns NULL there. Despite actually
saying "return NULL", that's right :-)

Perhaps you should change it to return "LCP" by default instead, and
not only on PID_LCP? It should silence the compiler.

This ppp_cp_event() is called in a few places:
- ppp_cp_parse_cr()
- ppp_rx()
- ppp_timer() (with a known protocol, though)
- and others, with PID_LCP.

Now, before printing proto_name(pid), ppp_cp_event() does
proto = get_proto(pid), and dereferences it :-)

The pid seems to always come from ppp_rx(). Fortunately it's checked
at start, and it case of an unknown proto it goes straight to rx_error.
-- 
Krzysztof "Chris" Hałasa

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