[PATCH 5.7 063/112] security: Fix hook iteration and default value for inode_copy_up_xattr

Greg Kroah-Hartman
2020-07-07T15:26:21Z

From: KP Singh <kpsingh@google.com>

[ Upstream commit 23e390cdbe6f85827a43d38f9288dcd3066fa376 ]

inode_copy_up_xattr returns 0 to indicate the acceptance of the xattr
and 1 to reject it. If the LSM does not know about the xattr, it's
expected to return -EOPNOTSUPP, which is the correct default value for
this hook. BPF LSM, currently, uses 0 as the default value and thereby
falsely allows all overlay fs xattributes to be copied up.

The iteration logic is also updated from the "bail-on-fail"
call_int_hook to continue on the non-decisive -EOPNOTSUPP and bail out
on other values.

Fixes: 98e828a0650f ("security: Refactor declaration of LSM hooks")
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: James Morris <jmorris@namei.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/lsm_hook_defs.h | 2 +-
security/security.c | 17 ++++++++++++++++-
2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 5616b2567aa7f..c2d073c49bf8a 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -149,7 +149,7 @@ LSM_HOOK(int, 0, inode_listsecurity, struct inode *inode, char *buffer,
size_t buffer_size)
LSM_HOOK(void, LSM_RET_VOID, inode_getsecid, struct inode *inode, u32 *secid)
LSM_HOOK(int, 0, inode_copy_up, struct dentry *src, struct cred **new)
-LSM_HOOK(int, 0, inode_copy_up_xattr, const char *name)
+LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, const char *name)
LSM_HOOK(int, 0, kernfs_init_security, struct kernfs_node *kn_dir,
struct kernfs_node *kn)
LSM_HOOK(int, 0, file_permission, struct file *file, int mask)
diff --git a/security/security.c b/security/security.c
index 51de970fbb1ed..8b4d342ade5e1 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1409,7 +1409,22 @@ 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);
+ struct security_hook_list *hp;
+ int rc;
+
+ /*
+ * The implementation can return 0 (accept the xattr), 1 (discard the
+ * xattr), -EOPNOTSUPP if it does not know anything about the xattr or
+ * any other error code incase of an error.
+ */
+ hlist_for_each_entry(hp,
+ &security_hook_heads.inode_copy_up_xattr, list) {
+ rc = hp->hook.inode_copy_up_xattr(name);
+ if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
+ return rc;
+ }
+
+ return LSM_RET_DEFAULT(inode_copy_up_xattr);
}
EXPORT_SYMBOL(security_inode_copy_up_xattr);

--
2.25.1