* [PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs_whiteout
@ 2018-08-28 16:53 Mark Salyzyn
2018-08-28 17:43 ` Amir Goldstein
0 siblings, 1 reply; 4+ messages in thread
From: Mark Salyzyn @ 2018-08-28 16:53 UTC (permalink / raw)
To: linux-kernel
Cc: Mark Salyzyn, Miklos Szeredi, Jonathan Corbet, Vivek Goyal,
Eric W . Biederman, Amir Goldstein, Randy Dunlap,
Stephen Smalley, linux-unionfs, linux-doc
Assumption never checked, should fail if the mounter creds are not
sufficient.
Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: linux-unionfs@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
v5
- dependency of "overlayfs: override_creds=off option bypass creator_cred"
---
fs/overlayfs/overlayfs.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 7538b9b56237..bf3a80157d42 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -176,7 +176,7 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
{
- int err = vfs_whiteout(dir, dentry);
+ int err = capable(CAP_MKNOD) ? vfs_whiteout(dir, dentry) : -EPERM;
pr_debug("whiteout(%pd2) = %i\n", dentry, err);
return err;
}
--
2.19.0.rc0.228.g281dcd1b4d0-goog
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs_whiteout
2018-08-28 16:53 [PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs_whiteout Mark Salyzyn
@ 2018-08-28 17:43 ` Amir Goldstein
2018-08-28 18:42 ` Amir Goldstein
0 siblings, 1 reply; 4+ messages in thread
From: Amir Goldstein @ 2018-08-28 17:43 UTC (permalink / raw)
To: Mark Salyzyn
Cc: linux-kernel, Miklos Szeredi, Jonathan Corbet, Vivek Goyal,
Eric W. Biederman, Randy Dunlap, Stephen Smalley, overlayfs,
linux-doc
On Tue, Aug 28, 2018 at 7:53 PM Mark Salyzyn <salyzyn@android.com> wrote:
>
> Assumption never checked, should fail if the mounter creds are not
> sufficient.
>
> Signed-off-by: Mark Salyzyn <salyzyn@android.com>
> Cc: Miklos Szeredi <miklos@szeredi.hu>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Amir Goldstein <amir73il@gmail.com>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Cc: Stephen Smalley <sds@tycho.nsa.gov>
> Cc: linux-unionfs@vger.kernel.org
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
>
> v5
> - dependency of "overlayfs: override_creds=off option bypass creator_cred"
> ---
> fs/overlayfs/overlayfs.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 7538b9b56237..bf3a80157d42 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -176,7 +176,7 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
>
> static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
> {
> - int err = vfs_whiteout(dir, dentry);
> + int err = capable(CAP_MKNOD) ? vfs_whiteout(dir, dentry) : -EPERM;
Should that be ns_capable()? Should the test go into vfs_whiteout()?
I feel there is no convention at all.
Thanks,
Amir.
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs_whiteout
2018-08-28 17:43 ` Amir Goldstein
@ 2018-08-28 18:42 ` Amir Goldstein
2018-08-28 18:51 ` Mark Salyzyn
0 siblings, 1 reply; 4+ messages in thread
From: Amir Goldstein @ 2018-08-28 18:42 UTC (permalink / raw)
To: Mark Salyzyn
Cc: linux-kernel, Miklos Szeredi, Jonathan Corbet, Vivek Goyal,
Eric W. Biederman, Randy Dunlap, Stephen Smalley, overlayfs,
linux-doc
On Tue, Aug 28, 2018 at 8:43 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Tue, Aug 28, 2018 at 7:53 PM Mark Salyzyn <salyzyn@android.com> wrote:
> >
> > Assumption never checked, should fail if the mounter creds are not
> > sufficient.
> >
> > Signed-off-by: Mark Salyzyn <salyzyn@android.com>
> > Cc: Miklos Szeredi <miklos@szeredi.hu>
> > Cc: Jonathan Corbet <corbet@lwn.net>
> > Cc: Vivek Goyal <vgoyal@redhat.com>
> > Cc: Eric W. Biederman <ebiederm@xmission.com>
> > Cc: Amir Goldstein <amir73il@gmail.com>
> > Cc: Randy Dunlap <rdunlap@infradead.org>
> > Cc: Stephen Smalley <sds@tycho.nsa.gov>
> > Cc: linux-unionfs@vger.kernel.org
> > Cc: linux-doc@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> >
> > v5
> > - dependency of "overlayfs: override_creds=off option bypass creator_cred"
> > ---
> > fs/overlayfs/overlayfs.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> > index 7538b9b56237..bf3a80157d42 100644
> > --- a/fs/overlayfs/overlayfs.h
> > +++ b/fs/overlayfs/overlayfs.h
> > @@ -176,7 +176,7 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
> >
> > static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
> > {
> > - int err = vfs_whiteout(dir, dentry);
> > + int err = capable(CAP_MKNOD) ? vfs_whiteout(dir, dentry) : -EPERM;
>
> Should that be ns_capable()? Should the test go into vfs_whiteout()?
> I feel there is no convention at all.
>
Nevermind, I don't think creating a whiteout poses any risk, so don't think
we need to worry about CAP_MKNOD.
Thanks,
Amir.
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs_whiteout
2018-08-28 18:42 ` Amir Goldstein
@ 2018-08-28 18:51 ` Mark Salyzyn
0 siblings, 0 replies; 4+ messages in thread
From: Mark Salyzyn @ 2018-08-28 18:51 UTC (permalink / raw)
To: Amir Goldstein
Cc: linux-kernel, Miklos Szeredi, Jonathan Corbet, Vivek Goyal,
Eric W. Biederman, Randy Dunlap, Stephen Smalley, overlayfs,
linux-doc
On 08/28/2018 11:42 AM, Amir Goldstein wrote:
> On Tue, Aug 28, 2018 at 8:43 PM Amir Goldstein <amir73il@gmail.com> wrote:
>> On Tue, Aug 28, 2018 at 7:53 PM Mark Salyzyn <salyzyn@android.com> wrote:
>>> Assumption never checked, should fail if the mounter creds are not
>>> sufficient.
>>>
>>> Signed-off-by: Mark Salyzyn <salyzyn@android.com>
>>> Cc: Miklos Szeredi <miklos@szeredi.hu>
>>> Cc: Jonathan Corbet <corbet@lwn.net>
>>> Cc: Vivek Goyal <vgoyal@redhat.com>
>>> Cc: Eric W. Biederman <ebiederm@xmission.com>
>>> Cc: Amir Goldstein <amir73il@gmail.com>
>>> Cc: Randy Dunlap <rdunlap@infradead.org>
>>> Cc: Stephen Smalley <sds@tycho.nsa.gov>
>>> Cc: linux-unionfs@vger.kernel.org
>>> Cc: linux-doc@vger.kernel.org
>>> Cc: linux-kernel@vger.kernel.org
>>>
>>> v5
>>> - dependency of "overlayfs: override_creds=off option bypass creator_cred"
>>> ---
>>> fs/overlayfs/overlayfs.h | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
>>> index 7538b9b56237..bf3a80157d42 100644
>>> --- a/fs/overlayfs/overlayfs.h
>>> +++ b/fs/overlayfs/overlayfs.h
>>> @@ -176,7 +176,7 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
>>>
>>> static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
>>> {
>>> - int err = vfs_whiteout(dir, dentry);
>>> + int err = capable(CAP_MKNOD) ? vfs_whiteout(dir, dentry) : -EPERM;
>> Should that be ns_capable()? Should the test go into vfs_whiteout()?
>> I feel there is no convention at all.
>>
> Nevermind, I don't think creating a whiteout poses any risk, so don't think
> we need to worry about CAP_MKNOD.
>
> Thanks,
> Amir.
Ok, will discard from the set, we can address this later if it creates
concern (as in, not a dependency to my proposed feature flag). So we
feel that whiteout node in the writeable playground of workdir/upperdir
is not in itself a security concern. Other (more dangerous) mknod will
be checked against the caller's credentials coming in.
-- Mark
^ permalink raw reply [flat|nested] 4+ messages in thread
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2018-08-28 16:53 [PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs_whiteout Mark Salyzyn
2018-08-28 17:43 ` Amir Goldstein
2018-08-28 18:42 ` Amir Goldstein
2018-08-28 18:51 ` Mark Salyzyn
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