On Mon, Jul 11, 2016 at 11:24:26AM -0400, Stephen Smalley wrote:
> On 07/08/2016 12:19 PM, Vivek Goyal wrote:
> > Provide a security hook to label new file correctly when a file is copied
> > up from lower layer to upper layer of a overlay/union mount.
> >
> > This hook can prepare a new set of creds which are suitable for new file
> > creation during copy up. Caller will use new creds to create file and then
> > revert back to old creds and release new creds.
> >
> > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> > ---
> > fs/overlayfs/copy_up.c | 18 ++++++++++++++++++
> > include/linux/lsm_hooks.h | 11 +++++++++++
> > include/linux/security.h | 6 ++++++
> > security/security.c | 8 ++++++++
> > 4 files changed, 43 insertions(+)
> >
> > diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> > index 80aa6f1..8ebea18 100644
> > --- a/fs/overlayfs/copy_up.c
> > +++ b/fs/overlayfs/copy_up.c
> > @@ -246,6 +246,8 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
> > struct dentry *upper = NULL;
> > umode_t mode = stat->mode;
> > int err;
> > + const struct cred *old_creds = NULL;
> > + struct cred *new_creds = NULL;
> >
> > newdentry = ovl_lookup_temp(workdir, dentry);
> > err = PTR_ERR(newdentry);
> > @@ -258,10 +260,26 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
> > if (IS_ERR(upper))
> > goto out1;
> >
> > + err = security_inode_copy_up(dentry, &new_creds);
> > + if (err < 0) {
> > + if (new_creds)
> > + put_cred(new_creds);
>
> Why do we need a put_cred() here?
Being paranoid for the case of stacked modules. Say first module allocated
creds but second module returned error, in that case creds will have to
be freed.
I can get rid of it for now and if in future two LSMs implement this hook,
one can change it, if need be.
Thanks
Vivek
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