From: "Dmitry V. Levin" <ldv@altlinux.org>
To: Mark Wielaard <mark@klomp.org>
Cc: elfutils-devel@sourceware.org,
Florian Weimer <fweimer@redhat.com>,
Panu Matilainen <pmatilai@laiskiainen.org>
Subject: Re: [PATCH] elfclassify tool
Date: Fri, 19 Jul 2019 18:35:00 -0000 [thread overview]
Message-ID: <20190719183542.GB29323@altlinux.org> (raw)
In-Reply-To: <84da918d32c57e6f16fbcf1c854b375111dbdcb5.camel@wildebeest.org>
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On Fri, Jul 19, 2019 at 04:21:53PM +0200, Mark wrote:
> On Fri, 2019-07-19 at 16:43 +0300, Dmitry V. Levin wrote:
> > On Fri, Jul 19, 2019 at 02:47:09PM +0200, Mark Wielaard wrote:
> > [...]
> > > +static bool
> > > +is_shared (void)
> > > +{
> > > + if (!is_loadable ())
> > > + return false;
> > > +
> > > + /* The ELF type is very clear: this is an executable. */
> > > + if (elf_type == ET_EXEC)
> > > + return false;
> > > +
> > > + /* If the object is marked as PIE, it is definitely an
> > > executable,
> > > + and not a loadlable shared object. */
> > > + if (has_pie_flag)
> > > + return false;
> > > +
> > > + /* Treat a DT_SONAME tag as a strong indicator that this is a
> > > shared
> > > + object. */
> > > + if (has_soname)
> > > + return true;
> >
> > I'm not sure DT_SONAME is a reliable indicator.
> >
> > I've seen many cases of DT_SONAME being erroneously applied to
> > non-libraries, e.g. lib.so was used as soname in openjdk executables.
>
> I didn't know. Is this really common?
I don't think it is very common, but the mistake is very easy to make
(-Wl,-soname,lib.so) and it doesn't really break anything. Apparently,
some projects apply the same linker flags that add DT_SONAME to all
generated files.
> I did find one java binary on my system that indeed has this problem.
> $ eu-readelf -d /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.212.b04-
> 0.el7_6.x86_64/jre/bin/policytool
>
> Dynamic segment contains 39 entries:
> Addr: 0x0000000000600d88 Offset: 0x000d88 Link to section: [ 7]
> '.dynstr'
> Type Value
> NEEDED Shared library: [libpthread.so.0]
> NEEDED Shared library: [libz.so.1]
> NEEDED Shared library: [libX11.so.6]
> NEEDED Shared library: [libjli.so]
> NEEDED Shared library: [libdl.so.2]
> NEEDED Shared library: [libc.so.6]
> SONAME Library soname: [lib.so]
> RPATH Library rpath:
> [$ORIGIN/../lib/amd64/jli:$ORIGIN/../lib/amd64]
> [...]
>
> But even so eu-elfclassify still doesn't treat it as a shared library,
> because:
> $ eu-elfclassify -v --shared policytool; echo $?
> info: policytool: ELF kind: ELF_K_ELF (0x3)
> info: policytool: ELF type: ET_EXEC (0x2)
> info: policytool: PT_LOAD found
> info: policytool: allocated PROGBITS section found
> info: policytool: program interpreter found
> info: policytool: dynamic segment found
> info: policytool: soname found
> info: policytool: DT_DEBUG found
> 1
>
> So other characteristics like it being ET_EXEC mark it as an
> executable. And I assume if it was PIE (ET_DYN) the PIE DT_FLAGS would
> have caught it.
Yes, the checks above has_soname are much more definitive.
> So, I don't think the code is wrong. We might want to tweak the comment
> a bit though, to make it less definitive?
What I'm saying is that has_soname is just a hint which is probably even
less reliable than has_program_interpreter.
--
ldv
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next prev parent reply other threads:[~2019-07-19 18:35 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-12 15:38 Florian Weimer
2019-04-15 15:39 ` Mark Wielaard
2019-04-16 11:38 ` Florian Weimer
2019-04-18 11:17 ` Florian Weimer
2019-07-19 12:47 ` Mark Wielaard
2019-07-19 13:43 ` Dmitry V. Levin
2019-07-19 14:21 ` Mark
2019-07-19 18:35 ` Dmitry V. Levin [this message]
2019-07-19 21:00 ` Florian Weimer
2019-07-19 21:23 ` Dmitry V. Levin
2019-07-19 21:36 ` Mark Wielaard
2019-07-19 22:57 ` Dmitry V. Levin
2019-07-20 21:51 ` Mark Wielaard
2019-07-25 22:39 ` [PATCH] elfclassify: Add --library classification Mark Wielaard
2019-07-26 22:53 ` Dmitry V. Levin
2019-07-26 23:04 ` [PATCH] elfclassify tool Dmitry V. Levin
2019-07-27 11:54 ` Mark Wielaard
2019-07-20 21:40 ` Mark Wielaard
2019-07-22 15:55 ` Florian Weimer
2019-07-26 22:11 ` Mark Wielaard
2019-07-29 8:44 ` Florian Weimer
2019-07-29 14:24 ` Mark Wielaard
2019-08-11 23:38 ` Mark Wielaard
2019-08-12 8:14 ` Florian Weimer
2019-08-12 15:18 ` Mark Wielaard
2019-07-29 9:16 ` Florian Weimer
2019-07-29 14:34 ` Mark Wielaard
2019-07-29 14:38 ` Florian Weimer
2019-08-13 9:44 ` Mark Wielaard
2019-08-13 11:42 ` Mark Wielaard
2019-08-14 20:46 ` [PATCH] config/elfutils.spec.in: package eu-elfclassify Dmitry V. Levin
2019-08-15 7:33 ` Mark Wielaard
2019-07-29 9:22 ` [PATCH] elfclassify tool Florian Weimer
2019-07-29 14:40 ` Mark Wielaard
2019-07-29 14:42 ` Florian Weimer
2019-07-19 13:24 ` Mark Wielaard
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