kernel/fs: Introduce check_write_stat_permissions utility method.

Like check_access_permissions() but for write_stat() hook instead
of access().

Basic logic copied from BFS, but with the UID/GID logic rewritten
to better conform to behavior on other OSes: notably, we allow
chown() requests that keep the UID the same to go through, same
as Linux seems to, which should fix #19666. We now also validate
that the GID is one of the current team's groups.

headers/os/drivers/fs_interface.h

@@ -331,8 +331,11 @@ extern status_t unremove_vnode(fs_volume* volume, ino_t vnodeID);
 extern status_t get_vnode_removed(fs_volume* volume, ino_t vnodeID,
 					bool* _removed);
 extern fs_volume* volume_for_vnode(fs_vnode* vnode);
+
 extern status_t check_access_permissions(int accessMode, mode_t mode,
 					gid_t nodeGroupID, uid_t nodeUserID);
+extern status_t check_write_stat_permissions(gid_t nodeGroupID, uid_t nodeUserID,
+					mode_t nodeMode, uint32 mask, const struct stat* stat);
 
 extern status_t read_pages(int fd, off_t pos, const struct iovec* vecs,
 					size_t count, size_t* _numBytes);

headers/private/fs_shell/fssh_api_wrapper.h

@@ -950,6 +950,7 @@
 #define get_vnode_removed			fssh_get_vnode_removed
 #define volume_for_vnode			fssh_volume_for_vnode
 #define check_access_permissions	fssh_check_access_permissions
+#define check_write_stat_permissions fssh_check_write_stat_permissions
 #define read_pages					fssh_read_pages
 #define write_pages					fssh_write_pages
 #define read_file_io_vec_pages		fssh_read_file_io_vec_pages

headers/private/fs_shell/fssh_fs_interface.h

@@ -364,6 +364,9 @@ extern fssh_fs_volume* fssh_volume_for_vnode(fssh_fs_vnode *vnode);
 extern fssh_status_t fssh_check_access_permissions(int accessMode,
 				fssh_mode_t mode, fssh_gid_t nodeGroupID,
 				fssh_uid_t nodeUserID);
+extern fssh_status_t fssh_check_write_stat_permissions(fssh_gid_t nodeGroupID,
+				fssh_uid_t nodeUserID, fssh_mode_t nodeMode, uint32_t mask,
+				const struct fssh_stat* stat);
 
 extern fssh_status_t fssh_read_pages(int fd, fssh_off_t pos,
 				const struct fssh_iovec *vecs, fssh_size_t count,

src/system/kernel/fs/vfs.cpp

@@ -4007,6 +4007,53 @@ check_access_permissions(int accessMode, mode_t mode, gid_t nodeGroupID,
 }
 
 
+extern "C" status_t
+check_write_stat_permissions(gid_t nodeGroupID, uid_t nodeUserID, mode_t nodeMode,
+	uint32 mask, const struct stat* stat)
+{
+	uid_t uid = geteuid();
+
+	// root has all permissions
+	if (uid == 0)
+		return B_OK;
+
+	const bool hasWriteAccess = check_access_permissions(W_OK,
+		nodeMode, nodeGroupID, nodeUserID) == B_OK;
+
+	if ((mask & B_STAT_SIZE) != 0) {
+		if (!hasWriteAccess)
+			return B_NOT_ALLOWED;
+	}
+
+	if ((mask & B_STAT_UID) != 0) {
+		if (nodeUserID == uid && stat->st_uid == uid) {
+			// No change.
+		} else
+			return B_NOT_ALLOWED;
+	}
+
+	if ((mask & B_STAT_GID) != 0) {
+		if (nodeUserID != uid)
+			return B_NOT_ALLOWED;
+
+		if (!is_in_group(thread_get_current_thread()->team, stat->st_gid))
+			return B_NOT_ALLOWED;
+	}
+
+	if ((mask & B_STAT_MODE) != 0) {
+		if (nodeUserID != uid)
+			return B_NOT_ALLOWED;
+	}
+
+	if ((mask & (B_STAT_CREATION_TIME | B_STAT_MODIFICATION_TIME | B_STAT_CHANGE_TIME)) != 0) {
+		if (!hasWriteAccess && nodeUserID != uid)
+			return B_NOT_ALLOWED;
+	}
+
+	return B_OK;
+}
+
+
 #if 0
 extern "C" status_t
 read_pages(int fd, off_t pos, const iovec* vecs, size_t count,

src/tools/fs_shell/vfs.cpp

@@ -24,6 +24,7 @@
 #include "fssh_fs_volume.h"
 #include "fssh_kernel_export.h"
 #include "fssh_module.h"
+#include "fssh_node_monitor.h"
 #include "fssh_stat.h"
 #include "fssh_stdio.h"
 #include "fssh_string.h"
@@ -2167,6 +2168,54 @@ fssh_check_access_permissions(int accessMode, fssh_mode_t mode,
 }
 
 
+extern "C" fssh_status_t
+fssh_check_write_stat_permissions(fssh_gid_t nodeGroupID, fssh_uid_t nodeUserID,
+	fssh_mode_t nodeMode, uint32_t mask, const struct fssh_stat* stat)
+{
+	uid_t uid = fssh_geteuid();
+
+	// root has all permissions
+	if (uid == 0)
+		return FSSH_B_OK;
+
+	const bool hasWriteAccess = fssh_check_access_permissions(FSSH_W_OK,
+		nodeMode, nodeGroupID, nodeUserID) == FSSH_B_OK;
+
+	if ((mask & FSSH_B_STAT_SIZE) != 0) {
+		if (!hasWriteAccess)
+			return FSSH_B_NOT_ALLOWED;
+	}
+
+	if ((mask & FSSH_B_STAT_UID) != 0) {
+		if (nodeUserID == uid && stat->fssh_st_uid == uid) {
+			// No change.
+		} else
+			return FSSH_B_NOT_ALLOWED;
+	}
+
+	if ((mask & FSSH_B_STAT_GID) != 0) {
+		if (nodeUserID != uid)
+			return FSSH_B_NOT_ALLOWED;
+
+		if (fssh_getegid() != stat->fssh_st_gid)
+			return FSSH_B_NOT_ALLOWED;
+	}
+
+	if ((mask & FSSH_B_STAT_MODE) != 0) {
+		if (nodeUserID != uid)
+			return FSSH_B_NOT_ALLOWED;
+	}
+
+	if ((mask & (FSSH_B_STAT_CREATION_TIME | FSSH_B_STAT_MODIFICATION_TIME
+			| FSSH_B_STAT_CHANGE_TIME)) != 0) {
+		if (!hasWriteAccess && nodeUserID != uid)
+			return FSSH_B_NOT_ALLOWED;
+	}
+
+	return FSSH_B_OK;
+}
+
+
 //! Works directly on the host's file system
 extern "C" fssh_status_t
 fssh_read_pages(int fd, fssh_off_t pos, const fssh_iovec *vecs,