[PATCH][capabilities-next] commoncap: move assignment of fs_ns to avoid null pointer dereference

[serge@hallyn.com (Serge E. Hallyn)]

Hi James,

it doesn't look like this has been picked up yet.  Assuming I'm not looking
in the wrong place, can you pull it into the security tree?

thanks,
-serge

Quoting Serge E. Hallyn (serge at hallyn.com):
> On Mon, Sep 04, 2017 at 06:50:05PM +0100, Colin King wrote:
> > From: Colin Ian King <colin.king@canonical.com>
> > 
> > The pointer fs_ns is assigned from inode->i_ib->s_user_ns before
> > a null pointer check on inode, hence if inode is actually null we
> > will get a null pointer dereference on this assignment. Fix this
> > by only dereferencing inode after the null pointer check on
> > inode.
> > 
> > Detected by CoverityScan CID#1455328 ("Dereference before null check")
> > 
> > Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities")
> > Signed-off-by: Colin Ian King <colin.king@canonical.com>
> 
> thanks!
> 
> Acked-by: Serge Hallyn <serge@hallyn.com>
> 
> > ---
> >  security/commoncap.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/security/commoncap.c b/security/commoncap.c
> > index c25e0d27537f..fc46f5b85251 100644
> > --- a/security/commoncap.c
> > +++ b/security/commoncap.c
> > @@ -585,13 +585,14 @@ int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data
> >  	struct vfs_ns_cap_data data, *nscaps = &data;
> >  	struct vfs_cap_data *caps = (struct vfs_cap_data *) &data;
> >  	kuid_t rootkuid;
> > -	struct user_namespace *fs_ns = inode->i_sb->s_user_ns;
> > +	struct user_namespace *fs_ns;
> >  
> >  	memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
> >  
> >  	if (!inode)
> >  		return -ENODATA;
> >  
> > +	fs_ns = inode->i_sb->s_user_ns;
> >  	size = __vfs_getxattr((struct dentry *)dentry, inode,
> >  			      XATTR_NAME_CAPS, &data, XATTR_CAPS_SZ);
> >  	if (size == -ENODATA || size == -EOPNOTSUPP)
> > -- 
> > 2.14.1
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