Re: dlsym(handle) may search in unrelated libraries

[Markus Wichmann <nullplan@gmx.net>]

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On Wed, Feb 06, 2019 at 08:02:28PM +0300, Alexey Izbyshev wrote:
> Unfortunately, my test case was a simplified example of a general problem:
> dso->deps is assigned only for the main app and for libraries opened with
> dlopen(), but not for their dependencies. Consider the following:

Right you are. It took me a while to understand what the deps array was
even for (since musl's dlclose() doesn't do anything, tracking
dependencies is mostly pointless), but I found it is needed for lazy
relocation processing. So it is necessary for all libs opened by
dlopen() directly to contain a list of all their dependencies. All the
other libs can have an empty list.

So I propose the attached patch in addition to the previous one. This
will set dso->deps to the empty list in all libs not directly loaded
from dlopen(). The previous patch is still necessary, as nothing ever
calls load_deps() on the libc or the vdso, but all other modules get a
load_deps() treatment.

> 
> Alexey
> 
> 

Ciao,
Markus

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From 841dd4e075040e2aeb01adea8ef5e2f7c0fc006a Mon Sep 17 00:00:00 2001
From: Markus Wichmann <nullplan@gmx.net>
Date: Wed, 6 Feb 2019 21:13:05 +0100
Subject: [PATCH 7/7] Initialize deps on non-directly loaded libs.

As pointed out by Alexey Izbyshev, having the deps member be zero opens
dlopen() and dlsym() up to malfunctions, if a library was previously
loaded as dependency and is then dlopen()ed. Therefore, we now set the
deps member of the dso descriptor to the sentry value in all libs loaded
as dependencies.
---
 ldso/dynlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index 6ffeca85..f8346c54 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -1158,8 +1158,8 @@ static void load_deps(struct dso *p)
 				*deps = tmp;
 			}
 		}
+		if (!p->deps) p->deps = (struct dso**)&nodeps_dummy;
 	}
-	if (!*deps) *deps = (struct dso **)&nodeps_dummy;
 }
 
 static void load_preload(char *s)
-- 
2.20.1