[PATCH RFC 1/3] security: introduce and use call_int_hook_ignore_default()

[Paolo Abeni <pabeni@redhat.com>]

The following hooks currently don't allow the LSM module to tell the
core to ignore its return code:

sb_set_mnt_opts
inode_init_security
inode_getsecctx
socket_getpeersec_stream
socket_getpeersec_dgram

because the return value for the security function when no LSMs are
loaded is non zero, and LSMs use the current LSM_RET_DEFAULT() (zero)
to represent "success".

Introduce a new variant of the call_int_hook() macros the explicitly
ignores the return code from the LSM when equal to LSM_RET_DEFAULT,
use it for the above hooks, and change the default to 1.

All the exiting LSM except BPF don't use such return value, so no
functional change is expected.

After this change, LSM returning the LSM_RET_DEFAULT value will become
a no-op for the mentioned hooks.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 include/linux/lsm_hook_defs.h | 10 ++++-----
 security/security.c           | 42 ++++++++++++++++++++++++++---------
 2 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 4f2621e87634..c9032e20d0b3 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -73,7 +73,7 @@ LSM_HOOK(int, 0, sb_mount, const char *dev_name, const struct path *path,
 LSM_HOOK(int, 0, sb_umount, struct vfsmount *mnt, int flags)
 LSM_HOOK(int, 0, sb_pivotroot, const struct path *old_path,
 	 const struct path *new_path)
-LSM_HOOK(int, 0, sb_set_mnt_opts, struct super_block *sb, void *mnt_opts,
+LSM_HOOK(int, 1, sb_set_mnt_opts, struct super_block *sb, void *mnt_opts,
 	 unsigned long kern_flags, unsigned long *set_kern_flags)
 LSM_HOOK(int, 0, sb_clone_mnt_opts, const struct super_block *oldsb,
 	 struct super_block *newsb, unsigned long kern_flags,
@@ -111,7 +111,7 @@ LSM_HOOK(int, 0, path_notify, const struct path *path, u64 mask,
 	 unsigned int obj_type)
 LSM_HOOK(int, 0, inode_alloc_security, struct inode *inode)
 LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode)
-LSM_HOOK(int, 0, inode_init_security, struct inode *inode,
+LSM_HOOK(int, 1, inode_init_security, struct inode *inode,
 	 struct inode *dir, const struct qstr *qstr, const char **name,
 	 void **value, size_t *len)
 LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode,
@@ -272,7 +272,7 @@ LSM_HOOK(void, LSM_RET_VOID, release_secctx, char *secdata, u32 seclen)
 LSM_HOOK(void, LSM_RET_VOID, inode_invalidate_secctx, struct inode *inode)
 LSM_HOOK(int, 0, inode_notifysecctx, struct inode *inode, void *ctx, u32 ctxlen)
 LSM_HOOK(int, 0, inode_setsecctx, struct dentry *dentry, void *ctx, u32 ctxlen)
-LSM_HOOK(int, 0, inode_getsecctx, struct inode *inode, void **ctx,
+LSM_HOOK(int, 1, inode_getsecctx, struct inode *inode, void **ctx,
 	 u32 *ctxlen)
 
 #if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
@@ -308,9 +308,9 @@ LSM_HOOK(int, 0, socket_getsockopt, struct socket *sock, int level, int optname)
 LSM_HOOK(int, 0, socket_setsockopt, struct socket *sock, int level, int optname)
 LSM_HOOK(int, 0, socket_shutdown, struct socket *sock, int how)
 LSM_HOOK(int, 0, socket_sock_rcv_skb, struct sock *sk, struct sk_buff *skb)
-LSM_HOOK(int, 0, socket_getpeersec_stream, struct socket *sock,
+LSM_HOOK(int, 1, socket_getpeersec_stream, struct socket *sock,
 	 sockptr_t optval, sockptr_t optlen, unsigned int len)
-LSM_HOOK(int, 0, socket_getpeersec_dgram, struct socket *sock,
+LSM_HOOK(int, 1, socket_getpeersec_dgram, struct socket *sock,
 	 struct sk_buff *skb, u32 *secid)
 LSM_HOOK(int, 0, sk_alloc_security, struct sock *sk, int family, gfp_t priority)
 LSM_HOOK(void, LSM_RET_VOID, sk_free_security, struct sock *sk)
diff --git a/security/security.c b/security/security.c
index 2dfc7b9f6ed9..b9a7b15e269e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -784,6 +784,23 @@ static int lsm_superblock_alloc(struct super_block *sb)
 	RC;							\
 })
 
+#define call_int_hook_ignore_default(FUNC, IRC, ...) ({		\
+	int TRC, RC = IRC;					\
+	do {							\
+		struct security_hook_list *P;			\
+								\
+		hlist_for_each_entry(P, &security_hook_heads.FUNC, list) { \
+			TRC = P->hook.FUNC(__VA_ARGS__);	\
+			if (TRC != LSM_RET_DEFAULT(FUNC))	\
+				continue;			\
+			RC = TRC;				\
+			if (RC != 0)				\
+				break;				\
+		}						\
+	} while (0);						\
+	RC;							\
+})
+
 /* Security operations */
 
 /**
@@ -1405,9 +1422,9 @@ int security_sb_set_mnt_opts(struct super_block *sb,
 			     unsigned long kern_flags,
 			     unsigned long *set_kern_flags)
 {
-	return call_int_hook(sb_set_mnt_opts,
-			     mnt_opts ? -EOPNOTSUPP : 0, sb,
-			     mnt_opts, kern_flags, set_kern_flags);
+	return call_int_hook_ignore_default(sb_set_mnt_opts,
+					    mnt_opts ? -EOPNOTSUPP : 0, sb,
+					    mnt_opts, kern_flags, set_kern_flags);
 }
 EXPORT_SYMBOL(security_sb_set_mnt_opts);
 
@@ -1612,11 +1629,13 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 		return 0;
 
 	if (!initxattrs)
-		return call_int_hook(inode_init_security, -EOPNOTSUPP, inode,
-				     dir, qstr, NULL, NULL, NULL);
+		return call_int_hook_ignore_default(inode_init_security,
+						    -EOPNOTSUPP, inode, dir,
+						    qstr, NULL, NULL, NULL);
 	memset(new_xattrs, 0, sizeof(new_xattrs));
 	lsm_xattr = new_xattrs;
-	ret = call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir, qstr,
+	ret = call_int_hook_ignore_default(inode_init_security, -EOPNOTSUPP,
+			    inode, dir, qstr,
 			    &lsm_xattr->name,
 			    &lsm_xattr->value,
 			    &lsm_xattr->value_len);
@@ -3973,7 +3992,8 @@ EXPORT_SYMBOL(security_inode_setsecctx);
  */
 int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
 {
-	return call_int_hook(inode_getsecctx, -EOPNOTSUPP, inode, ctx, ctxlen);
+	return call_int_hook_ignore_default(inode_getsecctx, -EOPNOTSUPP, inode,
+					    ctx, ctxlen);
 }
 EXPORT_SYMBOL(security_inode_getsecctx);
 
@@ -4330,8 +4350,8 @@ EXPORT_SYMBOL(security_sock_rcv_skb);
 int security_socket_getpeersec_stream(struct socket *sock, sockptr_t optval,
 				      sockptr_t optlen, unsigned int len)
 {
-	return call_int_hook(socket_getpeersec_stream, -ENOPROTOOPT, sock,
-			     optval, optlen, len);
+	return call_int_hook_ignore_default(socket_getpeersec_stream, -ENOPROTOOPT,
+					    sock, optval, optlen, len);
 }
 
 /**
@@ -4351,8 +4371,8 @@ int security_socket_getpeersec_stream(struct socket *sock, sockptr_t optval,
 int security_socket_getpeersec_dgram(struct socket *sock,
 				     struct sk_buff *skb, u32 *secid)
 {
-	return call_int_hook(socket_getpeersec_dgram, -ENOPROTOOPT, sock,
-			     skb, secid);
+	return call_int_hook_ignore_default(socket_getpeersec_dgram, -ENOPROTOOPT,
+					    sock, skb, secid);
 }
 EXPORT_SYMBOL(security_socket_getpeersec_dgram);
 
-- 
2.41.0