Re: [AppArmor 00/44] AppArmor security module overview

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On Jun 26, 2007, at 22:24:03, John Johansen wrote:
other issues that have been raised are:
- the use of d_path to generate the pathname used for mediation when a
  file is opened.
  - Generating the pathname using a reverse walk is considered ugly

A little more than "ugly". In this basic concurrent rename() and path-lookup load:

mkdir -p /a/b/0
mkdir -p /a/b/2
mkdir -p /c
touch /a/b/0/1

cd /a/b
while true; mv 0/1 2/3; mv 2/3 0/1; done &
cd /
while true; do mv a/b c/d; mv c/d a/b; done &
while true; do cat a/b/0/1 & done
while true; do cat a/b/2/3 & done
while true; do cat c/d/0/1 & done
while true; do cat c/d/2/3 & done

I seem to recall you could actually end up racing and building a path to the file in those directories as "a/d/0/3" or some other path at which it never even remotely existed. I'd love to be wrong, but I can't help but see this problem in any reverse-pathname-generation proposal which gets the locking right.

Cheers,
Kyle Moffett

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