[arch-general] Opening symlinks in tmpfs as root fails!

[Mohammad_AlSaleh]

On Tue, Dec 30, 2014 at 02:02:32PM +0100, Christian Hesse wrote:
> Christian Hesse <list at eworm.de> on Tue, 2014/12/30 13:42:
> > Mohammad_AlSaleh <ce.mohammad.alsaleh at gmail.com> on Tue, 2014/12/30 14:36:
> > > Hello.
> > > 
> > > I just came across some weird behavior.
> > > 
> > > A small testcase:
> > > 
> > > cd /tmp # should be tmpfs
> > > touch tfile
> > > ln -s tfile tlink
> > > cat tlink
> > > 
> > > When cat executes, it returns with success(0). But, if cat is executed
> > > as root, it fails with a permission denied error.
> > > 
> > > What's really happening is, the open() syscall fails with EACCESS when
> > > the file is a symlink in a tmpfs-mounted dir. But only fails when run
> > > as root!
> > > 
> > > I'm assuming this is a bug. Can anyone confirm it?
> > 
> > This is expected as /tmp has the sticky bit set.
> > 
> > https://wiki.ubuntu.com/Security/Features#Symlink_restrictions
> 
> As this was related to Ubuntu and pathes do not match... You can control the
> behavior via proc filesystem:
> 
> /proc/sys/fs/protected_symlinks
> 
> Or simply use sysctl:
> 
> sysctl -w fs.protected_symlinks=0
> 
> If you want to make this permanent add the entry to configuration file
> in /etc/sysctl.d/.

Thanks again.

Now that I understand what's going on, there is no need to change
the default behavior.

FWIW, I came across this behavior when I was testing a temporary local
repository. pacman failed to fetch repo_name.db which is a symlink
created by repo-add.

libcurl accesses the filesystem directly with file:// URLs. So, it
tried to open repo_name.db for reading and failed.

> -- 
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