From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_MSPIKE_H2,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 7924 invoked from network); 17 Aug 2022 19:29:12 -0000 Received: from second.openwall.net (193.110.157.125) by inbox.vuxu.org with ESMTPUTF8; 17 Aug 2022 19:29:12 -0000 Received: (qmail 16137 invoked by uid 550); 17 Aug 2022 19:29:08 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 16097 invoked from network); 17 Aug 2022 19:29:08 -0000 Date: Wed, 17 Aug 2022 15:28:55 -0400 From: Rich Felker To: James Y Knight Cc: musl@lists.openwall.com, elvis@edgedb.com Message-ID: <20220817192855.GD7074@brightrain.aerifal.cx> References: <3818608.tdWV9SEqCh@vulcan.edgedb.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] [PATCH] ldso/dynlink: Protect LD_ env vars from getting clobbered by apps On Wed, Aug 17, 2022 at 12:10:48PM -0400, James Y Knight wrote: > Sidenote: Linux does support a less awful way to change the kernel's view > of argv these days, using prctl(PR_SET_MM, PR_SET_MM_ARG_START (or _END), > addr, 0, 0). Sadly, it only allows root (CAP_SYS_RESOURCE) to use it. I'm > not sure why, perhaps that restriction could be relaxed for future > kernels... > > See > https://github.com/systemd/systemd/blob/87305b0fbfc0e40a948cf0a683bcf9d47b8a41a3/src/basic/process-util.c#L256 > for an example of use (including ugly workaround for the API being silly > and setting START/END with separate syscalls, but requiring START <= END at > all times) Yes, unfortunately (at least last I checked) it's also only available if CRIU support was enabled in the kernel since that's the only thing its creators envisioned it being used for... *sigh* > > On Wed, Aug 17, 2022 at 6:05 AM Elvis Pranskevichus > wrote: > > > There is no guarantee that the environment block will remain intact. > > For example, PostgreSQL clobbers argv/environ area to implement its > > "setproctitle" emulation on non-BSD [1], and there is a popular Python > > library inspired by it [2]. As a result, setting `LD_LIBRARY_PATH` > > or `LD_PRELOAD` has no effect on Postgres subprocesses when linking > > against musl. > > > > Protect against this by making a copies instead of storing the > > original pointers directly. > > > > (please CC me, I'm not subscribed to the list) > > > > --- > > ldso/dynlink.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/ldso/dynlink.c b/ldso/dynlink.c > > index cc677952..703342b8 100644 > > --- a/ldso/dynlink.c > > +++ b/ldso/dynlink.c > > @@ -1756,8 +1756,8 @@ void __dls3(size_t *sp, size_t *auxv) > > > > /* Only trust user/env if kernel says we're not suid/sgid */ > > if (!libc.secure) { > > - env_path = getenv("LD_LIBRARY_PATH"); > > - env_preload = getenv("LD_PRELOAD"); > > + env_path = strdup(getenv("LD_LIBRARY_PATH")); > > + env_preload = strdup(getenv("LD_PRELOAD")); > > } > > > > /* Activate error handler function */ > > > > > > > > > >