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From: ebiederm@xmission.com (Eric W. Biederman)
To: Miklos Szeredi <mszeredi@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	"Serge E . Hallyn" <serge@hallyn.com>,
	Tyler Hicks <code@tyhicks.com>
Subject: Re: [PATCH 0/2] capability conversion fixes
Date: Tue, 19 Jan 2021 15:10:14 -0600	[thread overview]
Message-ID: <87y2go8wg9.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20210119162204.2081137-1-mszeredi@redhat.com> (Miklos Szeredi's message of "Tue, 19 Jan 2021 17:22:02 +0100")

Miklos Szeredi <mszeredi@redhat.com> writes:

> It turns out overlayfs is actually okay wrt. mutliple conversions, because
> it uses the right context for lower operations.  I.e. before calling
> vfs_{set,get}xattr() on underlying fs, it overrides creds with that of the
> mounter, so the current user ns will now match that of
> overlay_sb->s_user_ns, meaning that the caps will be converted to just the
> right format for the next layer
>
> OTOH ecryptfs, which is the only other one affected by commit 7c03e2cda4a5
> ("vfs: move cap_convert_nscap() call into vfs_setxattr()") needs to be
> fixed up, since it doesn't do the cap override thing that overlayfs does.
>
> I don't have an ecryptfs setup, so untested, but it's a fairly trivial
> change.
>
> My other observation was that cap_inode_getsecurity() messes up conversion
> of caps in more than one case.  This is independent of the overlayfs user
> ns enablement but affects it as well.
>
> Maybe we can revisit the infrastructure improvements we discussed, but I
> think these fixes are more appropriate for the current cycle.

I mostly agree.  Fixing the bugs in a back-portable way is important.

However we need to sort out the infrastructure, and implementation.

As far as I can tell it is only the fact that overlayfs does not support
the new mount api aka fs_context that allows this fix to work and be
correct.

I believe the new mount api would allow specifying a different userns
thatn curent_user_ns for the overlay filesystem and that would break
this.

So while I agree with the making a minimal fix for now.  We need a good
fix because this code is much too subtle, and it can break very easily
with no one noticing.

Eric





> Thanks,
> Miklos
>
> Miklos Szeredi (2):
>   ecryptfs: fix uid translation for setxattr on security.capability
>   security.capability: fix conversions on getxattr
>
>  fs/ecryptfs/inode.c  | 10 +++++--
>  security/commoncap.c | 67 ++++++++++++++++++++++++++++----------------
>  2 files changed, 50 insertions(+), 27 deletions(-)

  parent reply	other threads:[~2021-01-19 21:12 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-19 16:22 [PATCH 0/2] capability conversion fixes Miklos Szeredi
2021-01-19 16:22 ` [PATCH 1/2] ecryptfs: fix uid translation for setxattr on security.capability Miklos Szeredi
2021-01-19 21:06   ` Eric W. Biederman
2021-01-20  7:52     ` Miklos Szeredi
2021-01-22 16:04       ` Tyler Hicks
2021-01-22 18:31   ` Tyler Hicks
2021-01-25 13:25     ` Miklos Szeredi
2021-01-25 13:46       ` Miklos Szeredi
2021-01-26  1:52       ` Tyler Hicks
2021-01-19 16:22 ` [PATCH 2/2] security.capability: fix conversions on getxattr Miklos Szeredi
2021-01-20  1:34   ` Eric W. Biederman
2021-01-20  7:58     ` Miklos Szeredi
2021-01-28 16:58     ` Serge E. Hallyn
2021-01-28 20:19       ` Eric W. Biederman
2021-01-28 20:38         ` Miklos Szeredi
2021-01-28 20:49           ` Eric W. Biederman
     [not found]         ` <20210129154839.GC1130@mail.hallyn.com>
2021-01-29 22:55           ` Eric W. Biederman
2021-01-30  2:06             ` Serge E. Hallyn
2021-01-31 18:14               ` Eric W. Biederman
     [not found]       ` <CAJfpegt34fO8tUw8R2_ZxxKHBdBO_-quf+-f3N8aZmS=1oRdvQ@mail.gmail.com>
     [not found]         ` <20210129153807.GA1130@mail.hallyn.com>
2021-01-29 23:11           ` Eric W. Biederman
2021-01-30  2:04             ` Serge E. Hallyn
2021-01-20 19:37   ` kernel test robot
2021-01-20 21:08   ` kernel test robot
2021-01-19 21:10 ` Eric W. Biederman [this message]
2021-01-20  7:39   ` [PATCH 0/2] capability conversion fixes Miklos Szeredi

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