linux-kernel - Re: [PATCH] modules: Fix corruption of /proc/kallsyms

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Date:   Mon, 11 Jul 2022 09:02:28 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Aaron Tomlin <atomlin@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] modules: Fix corruption of /proc/kallsyms

On Mon, Jul 11, 2022 at 10:48:16AM +0300, Adrian Hunter wrote:
> On 2/07/22 00:40, Luis Chamberlain wrote:
> > On Fri, Jul 01, 2022 at 12:44:03PM +0300, Adrian Hunter wrote:
> >> The commit 91fb02f31505 ("module: Move kallsyms support into a separate
> >> file") changed from using strlcpy() to using strscpy() which created a
> >> buffer overflow. That happened because:
> >>  1) an incorrect value was passed as the buffer length
> >>  2) strscpy() (unlike strlcpy()) may copy beyond the length of the
> >>     input string when copying word-by-word.
> >> The assumption was that because it was already known that the strings
> >> being copied would fit in the space available, it was not necessary
> >> to correctly set the buffer length.  strscpy() breaks that assumption
> >> because although it will not touch bytes beyond the given buffer length
> >> it may write bytes beyond the input string length when writing
> >> word-by-word.
> >>
> >> The result of the buffer overflow is to corrupt the symbol type
> >> information that follows. e.g.
> >>
> >>  $ sudo cat -v /proc/kallsyms | grep '\^' | head
> >>  ffffffffc0615000 ^@ rfcomm_session_get  [rfcomm]
> >>  ffffffffc061c060 ^@ session_list        [rfcomm]
> >>  ffffffffc06150d0 ^@ rfcomm_send_frame   [rfcomm]
> >>  ffffffffc0615130 ^@ rfcomm_make_uih     [rfcomm]
> >>  ffffffffc07ed58d ^@ bnep_exit   [bnep]
> >>  ffffffffc07ec000 ^@ bnep_rx_control     [bnep]
> >>  ffffffffc07ec1a0 ^@ bnep_session        [bnep]
> >>  ffffffffc07e7000 ^@ input_leds_event    [input_leds]
> >>  ffffffffc07e9000 ^@ input_leds_handler  [input_leds]
> >>  ffffffffc07e7010 ^@ input_leds_disconnect       [input_leds]
> >>
> >> Notably, the null bytes (represented above by ^@) can confuse tools.
> >>
> >> Fix by correcting the buffer length.
> >>
> >> Fixes: 91fb02f31505 ("module: Move kallsyms support into a separate file")
> >> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> > 
> > Queued up thanks!
> > 
> >   Luis
> 
> Thanks for processing this.
> 
> I notice it is -rc6 and I do not see it in Linus' tree. This is a fix
> for a regression, shouldn't it be included in 5.19?

Yeah sorry this will get to Linus today.

  Luis