kernel: Add is_in_group(Team*) private utility method and use it in the VFS.

Slightly more efficient than using getegid() and getgroups().

While at it, make the user-group utility methods C++-only.

headers/private/kernel/usergroup.h

@@ -18,14 +18,16 @@ namespace BKernel {
 using BKernel::Team;
 
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 // kernel private functions
 
 void		inherit_parent_user_and_group(Team* team, Team* parent);
 status_t	update_set_id_user_and_group(Team* team, const char* file);
+bool		is_in_group(Team* team, gid_t gid);
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 // syscalls
 

src/system/kernel/fs/vfs.cpp

@@ -51,6 +51,7 @@
 #include <syscalls.h>
 #include <syscall_restart.h>
 #include <tracing.h>
+#include <usergroup.h>
 #include <util/atomic.h>
 #include <util/AutoLock.h>
 #include <util/ThreadAutoLock.h>
@@ -3622,23 +3623,6 @@ common_file_io_vec_pages(struct vnode* vnode, void* cookie,
 }
 
 
-static bool
-is_user_in_group(gid_t gid)
-{
-	if (gid == getegid())
-		return true;
-
-	gid_t groups[NGROUPS_MAX];
-	int groupCount = getgroups(NGROUPS_MAX, groups);
-	for (int i = 0; i < groupCount; i++) {
-		if (gid == groups[i])
-			return true;
-	}
-
-	return false;
-}
-
-
 static status_t
 free_io_context(io_context* context)
 {
@@ -4011,7 +3995,7 @@ check_access_permissions(int accessMode, mode_t mode, gid_t nodeGroupID,
 	} else if (uid == nodeUserID) {
 		// user is node owner
 		permissions = userPermissions;
-	} else if (is_user_in_group(nodeGroupID)) {
+	} else if (is_in_group(thread_get_current_thread()->team, nodeGroupID)) {
 		// user is in owning group
 		permissions = groupPermissions;
 	} else {

src/system/kernel/usergroup.cpp

@@ -162,7 +162,7 @@ common_setreuid(uid_t ruid, uid_t euid, bool setAllIfPrivileged, bool kernel)
 }
 
 
-ssize_t
+static ssize_t
 common_getgroups(int groupCount, gid_t* groupList, bool kernel)
 {
 	Team* team = thread_get_current_thread()->team;
@@ -288,6 +288,26 @@ update_set_id_user_and_group(Team* team, const char* file)
 }
 
 
+bool
+is_in_group(Team* team, gid_t gid)
+{
+	TeamLocker teamLocker(team);
+
+	if (team->effective_gid == gid)
+		return true;
+
+	if (team->supplementary_groups == NULL)
+		return false;
+
+	for (int i = 0; i < team->supplementary_groups->count; i++) {
+		if (gid == team->supplementary_groups->groups[i])
+			return true;
+	}
+
+	return false;
+}
+
+
 gid_t
 _kern_getgid(bool effective)
 {