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Date: Sun, 22 Nov 2020 22:34:01 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: realpath without procfs -- should be ready for inclusion

On Mon, Nov 23, 2020 at 12:17:27AM -0300, √Črico Nogueira wrote:
> On Sun Nov 22, 2020 at 11:03 PM -03, Alexey Izbyshev wrote:
> > On 2020-11-23 01:56, Rich Felker wrote:
> > > I originally considered keeping the procfs based version and only
> > > using the new one as a fallback, but I discovered there are cases
> > > (involving chroot, namespaces, etc.) where the answer from procfs is
> > > wrong and validating it requires basically the same procedure as
> > > implementing it manually (walking and performing readlink on each path
> > > component).
> > > 
> > Pity that the simple and fast procfs-based implementation goes away. Do
> > you have any specific example of a wrong answer from procfs at hand, or
> > at least a more specific direction to look at than just
> > "chroot/namespaces"?
> 
> bubblewrap (when driven by Flatpak) is one such software. Void carries
> a patch [1] with NetBSD's realpath impl to work around this. Without it,
> launching flatpak applications sometimes didn't work at all.
> 
> - [1] https://github.com/void-linux/void-packages/blob/da86d30391e2b3535e8f9dfae452d2b362887e41/srcpkgs/bubblewrap/patches/realpath-workaround.patch

FWIW this seems to be a reason for needing the real implementation
like proposed, but not a reason for getting rid of the proc-based code
path. The reasons for that I mostly covered in my reply.

Rich

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