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    SubjectRe: [PATCH 3/9] security,overlayfs: Provide security hook for copy up of xattrs for overlay file
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    On 07/13/2016 10:44 AM, 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 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.
    >
    > Signed-off-by: David Howells <dhowells@redhat.com>
    > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

    Acked-by: Stephen Smalley <sds@tycho.nsa.gov>

    > ---
    > 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..4a3b8bc 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)
    > +{
    > + return -EOPNOTSUPP;
    > +}
    > +
    > 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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