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Message-ID: <2277404e-d91a-7190-ccbd-96e668ea95dd@tycho.nsa.gov>
Date: Mon, 11 Jul 2016 11:31:47 -0400
From: Stephen Smalley <sds@...ho.nsa.gov>
To: Vivek Goyal <vgoyal@...hat.com>, miklos@...redi.hu,
pmoore@...hat.com, casey@...aufler-ca.com,
linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org,
linux-security-module@...r.kernel.org
Cc: dwalsh@...hat.com, dhowells@...hat.com, viro@...IV.linux.org.uk,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 3/7] security,overlayfs: Provide security hook for copy up
of xattrs for overlay file
On 07/08/2016 12:19 PM, Vivek Goyal wrote:
> Provide a security hook which is called when xattrs of a file are being
> copied up. This hook is called once for each xattr and LSM can return 0
> to access the xattr, 1 to reject xattr, -EOPNOTSUPP if none of the lsms
> claim to know xattr and a negative error code if something went terribly
> wrong.
0 if the security module wants the xattr to be copied up, 1 if the
security module wants the xattr to be discarded on the copy, -EOPNOTSUPP
if the security module does not handle/manage the xattr, or a -errno
upon an error.
>
> If 0 or -EOPNOTSUPP is returned, xattr will be copied up, if 1 is returned,
> xattr will not be copied up and if negative error code is returned, copy up
> will be aborted.
Not sure I understand the benefit of the 0 vs -EOPNOTSUPP distinction.
>
> Signed-off-by: David Howells <dhowells@...hat.com>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> ---
> fs/overlayfs/copy_up.c | 7 +++++++
> include/linux/lsm_hooks.h | 10 ++++++++++
> include/linux/security.h | 6 ++++++
> security/security.c | 8 ++++++++
> 4 files changed, 31 insertions(+)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index 8ebea18..68cefb2 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -103,6 +103,13 @@ retry:
> goto retry;
> }
>
> + error = security_inode_copy_up_xattr(name);
> + if (error < 0 && error != -EOPNOTSUPP)
> + break;
> + if (error == 1) {
> + error = 0;
> + continue; /* Discard */
> + }
> error = vfs_setxattr(new, name, value, size, 0);
> if (error)
> break;
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index c1f95be..84caead 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -410,6 +410,14 @@
> * @src indicates the union dentry of file that is being copied up.
> * @new pointer to pointer to return newly allocated creds.
> * Returns 0 on success or a negative error code on error.
> + * @inode_copy_up_xattr:
> + * Filter the xattrs being copied up when a unioned file is copied
> + * up from a lower layer to the union/overlay layer.
> + * @name indicates the name of the xattr.
> + * Returns 0 to accept the xattr, 1 to discard the xattr, -EOPNOTSUPP if
> + * security module does not know about attribute or a negative error code
> + * to abort the copy up. Note that the caller is responsible for reading
> + * and writing the xattrs as this hook is merely a filter.
> *
> * Security hooks for file operations
> *
> @@ -1435,6 +1443,7 @@ union security_list_options {
> size_t buffer_size);
> void (*inode_getsecid)(struct inode *inode, u32 *secid);
> int (*inode_copy_up) (struct dentry *src, struct cred **new);
> + int (*inode_copy_up_xattr) (const char *name);
>
> int (*file_permission)(struct file *file, int mask);
> int (*file_alloc_security)(struct file *file);
> @@ -1707,6 +1716,7 @@ struct security_hook_heads {
> struct list_head inode_listsecurity;
> struct list_head inode_getsecid;
> struct list_head inode_copy_up;
> + struct list_head inode_copy_up_xattr;
> struct list_head file_permission;
> struct list_head file_alloc_security;
> struct list_head file_free_security;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index c976d79..08d3191 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -283,6 +283,7 @@ int security_inode_setsecurity(struct inode *inode, const char *name, const void
> int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size);
> void security_inode_getsecid(struct inode *inode, u32 *secid);
> int security_inode_copy_up(struct dentry *src, struct cred **new);
> +int security_inode_copy_up_xattr(const char *name);
> int security_file_permission(struct file *file, int mask);
> int security_file_alloc(struct file *file);
> void security_file_free(struct file *file);
> @@ -764,6 +765,11 @@ static inline int security_inode_copy_up(struct dentry *src, struct cred **new)
> return 0;
> }
>
> +static inline int security_inode_copy_up_xattr(const char *name)
> +{
> + -EOPNOTSUPP;
return?
> +}
> +
> static inline int security_file_permission(struct file *file, int mask)
> {
> return 0;
> diff --git a/security/security.c b/security/security.c
> index 3d142aa..3321e31 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -733,6 +733,12 @@ int security_inode_copy_up(struct dentry *src, struct cred **new)
> }
> EXPORT_SYMBOL(security_inode_copy_up);
>
> +int security_inode_copy_up_xattr(const char *name)
> +{
> + return call_int_hook(inode_copy_up_xattr, -EOPNOTSUPP, name);
> +}
> +EXPORT_SYMBOL(security_inode_copy_up_xattr);
> +
> int security_file_permission(struct file *file, int mask)
> {
> int ret;
> @@ -1671,6 +1677,8 @@ struct security_hook_heads security_hook_heads = {
> LIST_HEAD_INIT(security_hook_heads.inode_getsecid),
> .inode_copy_up =
> LIST_HEAD_INIT(security_hook_heads.inode_copy_up),
> + .inode_copy_up_xattr =
> + LIST_HEAD_INIT(security_hook_heads.inode_copy_up_xattr),
> .file_permission =
> LIST_HEAD_INIT(security_hook_heads.file_permission),
> .file_alloc_security =
>
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