[Bug 1476662] Re: lxc-start symlink vulnerabilities may allow guest to read host filesystem, interfere with apparmor

[Daniel Kraft]

The problem lies in the ubuntu patch

http://archive.ubuntu.com/ubuntu/pool/main/l/lxc/lxc_1.0.7-0ubuntu0.5.debian.tar.gz

where this code

+	size_t start = croot ? strlen(croot) : 0;
+	if (strcmp(ws + start, target + start) != 0) {
+		ERROR("Mount onto %s resulted in %s\n", target, ws);
+		goto out;
+	}

in file 0003-CVE-2015-1335.patch checks if ws and start are the same.
According to the given error (which I forgot to paste above), ws and target ARE different:

lxc-start: utils.c: ensure_not_symlink: 1384 Mount onto /usr/lib/x86_64
-linux-gnu/lxc//proc resulted in /usr/lib/x86_64-linux-gnu/lxc/proc

So target is

  /usr/lib/x86_64-linux-gnu/lxc//proc

and ws is

   /usr/lib/x86_64-linux-gnu/lxc/proc

Any hints how we could prevent the double slashing? Or would you just
"clean up" the path somehow?

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https://bugs.launchpad.net/bugs/1476662

Title:
  lxc-start symlink vulnerabilities may allow guest to read host
  filesystem, interfere with apparmor

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