linux-kernel - Re: [patch] perf tool buffer overflow in perf_header__read_build

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Date:   Sun, 25 Aug 2019 11:33:02 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [patch] perf tool buffer overflow in perf_header__read_build_ids

Em Fri, Aug 23, 2019 at 04:42:47PM -0400, Vince Weaver escreveu:
> On Fri, 26 Jul 2019, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Jul 23, 2019 at 04:42:30PM -0400, Vince Weaver escreveu:
> > > my perf_tool_fuzzer has found another issue, this one a buffer overflow
> > > in perf_header__read_build_ids.  The build id filename is read in with a 
> > > filename length read from the perf.data file, but this can be longer than
> > > PATH_MAX which will smash the stack.
> > > 
> > > This might not be the right fix, not sure if filename should be NUL
> > > terminated or not.
> > > 
> > > Signed-off-by: Vince Weaver <vincent.weaver@...ne.edu>
> > > 
> > > diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> > > index c24db7f4909c..9a893a26e678 100644
> > > --- a/tools/perf/util/header.c
> > > +++ b/tools/perf/util/header.c
> > > @@ -2001,6 +2001,9 @@ static int perf_header__read_build_ids(struct perf_header *header,
> > >  			perf_event_header__bswap(&bev.header);
> > >  
> > >  		len = bev.header.size - sizeof(bev);
> > > +
> > > +		if (len>PATH_MAX) len=PATH_MAX;
> > > +
> > 
> > Humm, I wonder if we shouldn't just declare the whole file invalid like
> > you did with the previous patch?

> > >  		if (readn(input, filename, len) != len)
> > >  			goto out;
> > >  		/*
>  
> did we ever decide how to fix this issue?  Or were you waiting on a 
> followup patch from me?

Fell thru the cracks, but yeah, I was waiting for a patch, can you send
it?

- Arnaldo
 
> This is actually an exploitable security bug if you can convince someone 
> to run "perf" on an untrusted perf.data file.

Indeed, and in light of the current discussion about unprivileged eBPF I
think we should start dropping privileges in perf report, etc.

- Arnaldo