Re: [ANN] unionfs patchset-13 release

On Wed, 31 May 2006, André Braga wrote:

> A post scriptum to the original message:
>
> The buggy behaviour won't affect the host system, but the jail could well be 
> compromised. I also have this feeling that ACLs also aren't respected inside 
> jails or can be overwritten as easily as shown below

By "ACLs also aren't respected inside jails", do you mean, "ACLs don't work in 
jail", or do you mean, "ACLs don't work with unionfs"?  They are believed 
firmly to work with jail, and if you have evidence to the contrary, a PR 
pointer would be greatly appreciated so it can be investigated.

I don't know much about the behavior of unionfs, but if VOP_ACCESS is passed 
down properly through the stack, then ACLs should be implemented.  There might 
be problems if two file systems are stacked and have different access control 
models.  I don't know enough about unionfs to reason about how it does behave, 
or should behave.  Unionfs seems to violate the notion of POLA, so I'm not 
sure how much POLA will help :-).

Robert N M Watson

>
> Thanks,
> André
>
> ---------------------- 8< ----------------------
>
> Hi,
>
> Once again, thank you for your patch.
>
> I believe I have found a bug:
>
> If a file or directory has non-default flags and this directory is
> mounted below a target point, the resulting union will not preserve
> the directory flags. Worse, it will appear as if the file flags are
> preserved, but they are not and as soon as a file that should not be
> modified gets modified, the flags are reset to the default state on
> the union mount. This could pose a *serious* security breach for
> people running jails rooted on unionfs mounts, like I intended to.
>
> Test case:
> (discrepancies are marked by a line containing "**** NOTICE" and
> aligned to fixed-length font display)
>
> # cd /tmp
> # mkdir -p test/a test/b/bb test/b/cc
> # touch test/b/cc/dd
> # chflags schg test/b/bb/
> # chflags uappnd test/b/cc/dd
> # ls -Rlo
> total 2
> drwxr-xr-x  4 root  wheel  - 512 Apr 29 08:12 test
>
> ./test:
> total 4
> drwxr-xr-x  2 root  wheel  - 512 Apr 29 08:12 a
> drwxr-xr-x  4 root  wheel  - 512 Apr 29 08:12 b
>
> ./test/a:
> total 0
>
> ./test/b:
> total 4
> drwxr-xr-x  2 root  wheel  schg 512 Apr 29 08:12 bb
> **** NOTICE 1a             ^^^^    ****
> drwxr-xr-x  2 root  wheel  -    512 Apr 29 08:12 cc
>
> ./test/b/bb:
> total 0
>
> ./test/b/cc:
> total 0
> -rw-r--r--  1 root  wheel  uappnd 0 Apr 29 08:12 dd
> **** NOTICE 2a             ^^^^^^    ****
> # echo ee >test/b/cc/dd
> test/b/cc/dd: Operation not permitted.
> # echo ee >> test/b/cc/dd
> **** NOTICE: this is the intended behavior for the 'uappnd' flag ****
> # cat test/b/cc/dd
> ee
> #
> # mount_unionfs -c transparent -b test/b test/a
> # ls -Rlo
> total 2
> drwxr-xr-x  4 root  wheel  - 512 Apr 29 08:12 test
>
> ./test:
> total 4
> drwxr-xr-x  2 root  wheel  - 512 Apr 29 08:12 a
> drwxr-xr-x  4 root  wheel  - 512 Apr 29 08:12 b
>
> ./test/a:
> total 4
> drwxr-xr-x  2 root  wheel  - 512 Apr 29 08:12 bb
> **** NOTICE 1b            ^^^    ****
> drwxr-xr-x  2 root  wheel  - 512 Apr 29 08:12 cc
>
> ./test/a/bb:
> total 0
>
> ./test/a/cc:
> total 2
> -rw-r--r--  1 root  wheel  uappnd 3 Apr 29 08:15 dd
> **** NOTICE 2b (LOOKS OK)  ^^^^^^    ****
> ./test/b:
> total 4
> drwxr-xr-x  2 root  wheel  schg 512 Apr 29 08:12 bb
> drwxr-xr-x  2 root  wheel  -    512 Apr 29 08:12 cc
>
> ./test/b/bb:
> total 0
>
> ./test/b/cc:
> total 2
> -rw-r--r--  1 root  wheel  uappnd 3 Apr 29 08:15 dd
> # echo ff > test/a/cc/dd
> # cat test/a/cc/dd
> ff
> **** NOTICE: very wrong behavior for the 'uappnd' flag! ****
> # ls -lo test/a/cc/dd
> -rw-r--r--  1 root  wheel  - 3 Apr 29 08:20 test/a/cc/dd
> **** NOTICE 2c (NO FLAG!) ^^^    ****
> # echo gg >test/b/cc/hh
> # chflags schg test/b/cc/hh
> # rm test/b/cc/hh
> override rw-r--r--  root/wheel schg for test/b/cc/hh? yes
> rm: test/b/cc/hh: Operation not permitted
> **** NOTICE 3a    ^^^^^^^^^^^^^^^^^^^^^^^  ****
> # ls -lo test/a/cc/hh
> -rw-r--r--  1 root  wheel  schg 3 Apr 29 08:24 test/a/cc/hh
> **** NOTICE 3b             ^^^^    ****
> # rm test/a/cc/hh
> override rw-r--r--  root/wheel schg for test/a/cc/hh? yes
> **** NOTICE 3c (NO ERROR!)  ****
> # ls -lo test/a/cc/
> total 2
> -rw-r--r--  1 root  wheel  - 3 Apr 29 08:20 dd
> **** NOTICE 3d (the file is gone despite immutable flags seemingly set!) 
> ****
>
> End of test case
>
> It makes no difference to specify '-c tradicional'.
>
> I skimmed over the patch code and have noticed no file flags or
> director[y flags] are indeed [ever] copied to the shadow files.
> [Edit: spelling]
>
> I'd really appreciate if you could fix that for the patch version 12.
>
> Thank you very much!
> André
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