[PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC

@@ -39,6 +39,7 @@
 #include <linux/bitops.h>
 #include <linux/init_task.h>
 #include <linux/uaccess.h>
+#include <linux/sysctl.h>
 
 #include "internal.h"
 #include "mount.h"

@@ -411,10 +412,90 @@ static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
 	return 0;
 }
 
+#define OMAYEXEC_ENFORCE_NONE	0
+#define OMAYEXEC_ENFORCE_MOUNT	(1 << 0)
+#define OMAYEXEC_ENFORCE_FILE	(1 << 1)
+#define _OMAYEXEC_LAST		OMAYEXEC_ENFORCE_FILE
+#define _OMAYEXEC_MASK		((_OMAYEXEC_LAST << 1) - 1)
+
+#ifdef CONFIG_OMAYEXEC_STATIC
+const int sysctl_omayexec_enforce =
+#ifdef CONFIG_OMAYEXEC_ENFORCE_MOUNT
+	OMAYEXEC_ENFORCE_MOUNT |
+#endif
+#ifdef CONFIG_OMAYEXEC_ENFORCE_FILE
+	OMAYEXEC_ENFORCE_FILE |
+#endif
+	OMAYEXEC_ENFORCE_NONE;
+#else /* CONFIG_OMAYEXEC_STATIC */
+int sysctl_omayexec_enforce __read_mostly = OMAYEXEC_ENFORCE_NONE;
+#endif /* CONFIG_OMAYEXEC_STATIC */
+
+/*
+ * Handle open_mayexec_enforce sysctl
+ */
+#if defined(CONFIG_SYSCTL) && !defined(CONFIG_OMAYEXEC_STATIC)
+int proc_omayexec(struct ctl_table *table, int write, void __user *buffer,
+		size_t *lenp, loff_t *ppos)
+{
+	int error;
+
+	if (write) {
+		struct ctl_table table_copy;
+		int tmp_mayexec_enforce;
+
+		if (!capable(CAP_MAC_ADMIN))
+			return -EPERM;
+
+		tmp_mayexec_enforce = *((int *)table->data);
+		table_copy = *table;
+		/* Do not erase sysctl_omayexec_enforce. */
+		table_copy.data = &tmp_mayexec_enforce;
+		error = proc_dointvec(&table_copy, write, buffer, lenp, ppos);
+		if (error)
+			return error;
+
+		if ((tmp_mayexec_enforce | _OMAYEXEC_MASK) != _OMAYEXEC_MASK)
+			return -EINVAL;
+
+		*((int *)table->data) = tmp_mayexec_enforce;
+	} else {
+		error = proc_dointvec(table, write, buffer, lenp, ppos);
+		if (error)
+			return error;
+	}
+	return 0;
+}
+#endif
+
+/**
+ * omayexec_inode_permission - Check O_MAYEXEC before accessing an inode
+ *
+ * @inode: Inode to check permission on
+ * @mask: Right to check for (%MAY_OPENEXEC, %MAY_EXECMOUNT, %MAY_EXEC)
+ *
+ * Returns 0 if access is permitted, -EACCES otherwise.
+ */
+static inline int omayexec_inode_permission(struct inode *inode, int mask)
+{
+	if (!(mask & MAY_OPENEXEC))
+		return 0;
+
+	if ((sysctl_omayexec_enforce & OMAYEXEC_ENFORCE_MOUNT) &&
+			!(mask & MAY_EXECMOUNT))
+		return -EACCES;
+
+	if (sysctl_omayexec_enforce & OMAYEXEC_ENFORCE_FILE)
+		return generic_permission(inode, MAY_EXEC);
+
+	return 0;
+}
+
 /**
  * inode_permission - Check for access rights to a given inode
  * @inode: Inode to check permission on
- * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
+ * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC, %MAY_OPENEXEC,
+ *        %MAY_EXECMOUNT)
  *
  * Check for read/write/execute permissions on an inode.  We use fs[ug]id for
  * this, letting us set arbitrary permissions for filesystem access without

@@ -454,6 +535,10 @@ int inode_permission(struct inode *inode, int mask)
 	if (retval)
 		return retval;
 
+	retval = omayexec_inode_permission(inode, mask);
+	if (retval)
+		return retval;
+
 	return security_inode_permission(inode, mask);
 }
 EXPORT_SYMBOL(inode_permission);

@@ -83,6 +83,9 @@ extern int sysctl_protected_symlinks;
 extern int sysctl_protected_hardlinks;
 extern int sysctl_protected_fifos;
 extern int sysctl_protected_regular;
+#ifndef CONFIG_OMAYEXEC_STATIC
+extern int sysctl_omayexec_enforce;
+#endif
 
 typedef __kernel_rwf_t rwf_t;
 

@@ -3545,6 +3548,8 @@ int proc_nr_dentry(struct ctl_table *table, int write,
 		  void __user *buffer, size_t *lenp, loff_t *ppos);
 int proc_nr_inodes(struct ctl_table *table, int write,
 		   void __user *buffer, size_t *lenp, loff_t *ppos);
+int proc_omayexec(struct ctl_table *table, int write, void __user *buffer,
+		size_t *lenp, loff_t *ppos);
 int __init get_filesystem_list(char *buf);
 
 #define __FMODE_EXEC		((__force int) FMODE_EXEC)

@@ -1892,6 +1892,15 @@ static struct ctl_table fs_table[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= &two,
 	},
+#ifndef CONFIG_OMAYEXEC_STATIC
+	{
+		.procname       = "open_mayexec_enforce",
+		.data           = &sysctl_omayexec_enforce,
+		.maxlen         = sizeof(int),
+		.mode           = 0600,
+		.proc_handler   = proc_omayexec,
+	},
+#endif
 #if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)
 	{
 		.procname	= "binfmt_misc",

@@ -230,6 +230,32 @@ config STATIC_USERMODEHELPER_PATH
 	  If you wish for all usermode helper programs to be disabled,
 	  specify an empty string here (i.e. "").
 
+menuconfig OMAYEXEC_STATIC
+	tristate "Configure O_MAYEXEC behavior at build time"
+	---help---
+	  Enable to enforce O_MAYEXEC at build time, and disable the dedicated
+	  fs.open_mayexec_enforce sysctl.
+
+	  See Documentation/admin-guide/sysctl/fs.rst for more details.
+
+if OMAYEXEC_STATIC
+
+config OMAYEXEC_ENFORCE_MOUNT
+	bool "Mount restriction"
+	default y
+	---help---
+	  Forbid opening files with the O_MAYEXEC option if their underlying VFS is
+	  mounted with the noexec option or if their superblock forbids execution
+	  of its content (e.g., /proc).
+
+config OMAYEXEC_ENFORCE_FILE
+	bool "File permission restriction"
+	---help---
+	  Forbid opening files with the O_MAYEXEC option if they are not marked as
+	  executable for the current process (e.g., POSIX permissions).
+
+endif # OMAYEXEC_STATIC
+
 source "security/selinux/Kconfig"
 source "security/smack/Kconfig"
 source "security/tomoyo/Kconfig"