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SubjectRe: [PATCH v4] Introduce v3 namespaced file capabilities
Quoting Eric W. Biederman (ebiederm@xmission.com):
> "Serge E. Hallyn" <serge@hallyn.com> writes:
> > Changelog:
> [snip]
> > May 8, 2017:
> > . fix leaking dentry refcount in cap_inode_getsecurity
> >
> [snip]
> > +/*
> > + * getsecurity: We are called for security.* before any attempt to read the
> > + * xattr from the inode itself.
> > + *
> > + * This gives us a chance to read the on-disk value and convert it. If we
> > + * return -EOPNOTSUPP, then vfs_getxattr() will call the i_op handler.
> > + *
> > + * Note we are not called by vfs_getxattr_alloc(), but that is only called
> > + * by the integrity subsystem, which really wants the unconverted values -
> > + * so that's good.
> > + */
> > +int cap_inode_getsecurity(struct inode *inode, const char *name, void **buffer,
> > + bool alloc)
> > +{
> > + int size, ret;
> > + kuid_t kroot;
> > + uid_t root, mappedroot;
> > + char *tmpbuf = NULL;
> > + struct vfs_cap_data *cap;
> > + struct vfs_ns_cap_data *nscap;
> > + struct dentry *dentry;
> > + struct user_namespace *fs_ns;
> > +
> > + if (strcmp(name, "capability") != 0)
> > + return -EOPNOTSUPP;
> > +
> > + dentry = d_find_alias(inode);
> > + if (!dentry)
> > + return -EINVAL;
> > +
> > + size = sizeof(struct vfs_ns_cap_data);
> > + ret = (int) vfs_getxattr_alloc(dentry, XATTR_NAME_CAPS,
> > + &tmpbuf, size, GFP_NOFS);
> > + dput(dentry);
>
> This looks like a good fix but ouch! That interface is wrong.
>
> The dentry is needed because vfs_getxattr_alloc does:
> error = handler->get(handler, dentry, inode, name, NULL, 0);
>
> Which is has no business taking a dentry as xattrs are inode concepts.
>
> I have no issue with your patch but it looks like that handler issue
> is going to need to be fixed with xattrs.

True, it's a bit clunky.

Any reason not to just have the current vfs_getxattr_alloc() become a
lightweight wrapper calling inode_getxattr_alloc(dentry->d_inode)?

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