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security: Fix hook iteration and default value for inode_copy_up_xattr

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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: 98e828a065 ("security: Refactor declaration of LSM hooks")
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: James Morris <jmorris@namei.org>
This commit is contained in:
KP Singh 2020-06-22 00:21:35 +02:00 committed by James Morris
parent 4bc799dcb6
commit 23e390cdbe
2 changed files with 17 additions and 2 deletions
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2
include/linux/lsm_hook_defs.h
View File

@ -150,7 +150,7 @@ 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)

17
security/security.c
View File

@ -1414,7 +1414,22 @@ 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);