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SubjectRe: [PATCH v4] Introduce v3 namespaced file capabilities
"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.

Eric

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