linux-kernel - [PATCH v4 6/6] mm/memfd: security hook for memfd

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Message-Id: <20221206150233.1963717-7-jeffxu@google.com>
Date:   Tue,  6 Dec 2022 15:02:33 +0000
From:   jeffxu@...omium.org
To:     skhan@...uxfoundation.org, keescook@...omium.org
Cc:     akpm@...ux-foundation.org, dmitry.torokhov@...il.com,
        dverkamp@...omium.org, hughd@...gle.com, jeffxu@...gle.com,
        jorgelo@...omium.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        jannh@...gle.com, linux-hardening@...r.kernel.org,
        Jeff Xu <jeffxu@...omium.org>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH v4 6/6] mm/memfd: security hook for memfd_create

From: Jeff Xu <jeffxu@...omium.org>

The new security_memfd_create allows lsm to check flags of
memfd_create.

The security by default system (such as chromeos) can use this
to implement system wide lsm to allow only non-executable memfd
being created.

Signed-off-by: Jeff Xu <jeffxu@...omium.org>
Reported-by: kernel test robot <lkp@...el.com>
---
 include/linux/lsm_hook_defs.h |  1 +
 include/linux/lsm_hooks.h     |  4 ++++
 include/linux/security.h      |  6 ++++++
 mm/memfd.c                    |  5 +++++
 security/security.c           | 13 +++++++++++++
 5 files changed, 29 insertions(+)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index ec119da1d89b..fd40840927c8 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -164,6 +164,7 @@ LSM_HOOK(int, 0, file_alloc_security, struct file *file)
 LSM_HOOK(void, LSM_RET_VOID, file_free_security, struct file *file)
 LSM_HOOK(int, 0, file_ioctl, struct file *file, unsigned int cmd,
 	 unsigned long arg)
+LSM_HOOK(int, 0, memfd_create, char *name, unsigned int flags)
 LSM_HOOK(int, 0, mmap_addr, unsigned long addr)
 LSM_HOOK(int, 0, mmap_file, struct file *file, unsigned long reqprot,
 	 unsigned long prot, unsigned long flags)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 4ec80b96c22e..5a18a6552278 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -543,6 +543,10 @@
  *	simple integer value.  When @arg represents a user space pointer, it
  *	should never be used by the security module.
  *	Return 0 if permission is granted.
+ * @memfd_create:
+ *	@name is the name of memfd file.
+ *	@flags is the flags used in memfd_create.
+ *	Return 0 if permission is granted.
  * @mmap_addr :
  *	Check permissions for a mmap operation at @addr.
  *	@addr contains virtual address that will be used for the operation.
diff --git a/include/linux/security.h b/include/linux/security.h
index ca1b7109c0db..5b87a780822a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -384,6 +384,7 @@ int security_file_permission(struct file *file, int mask);
 int security_file_alloc(struct file *file);
 void security_file_free(struct file *file);
 int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
+int security_memfd_create(char *name, unsigned int flags);
 int security_mmap_file(struct file *file, unsigned long prot,
 			unsigned long flags);
 int security_mmap_addr(unsigned long addr);
@@ -963,6 +964,11 @@ static inline int security_file_ioctl(struct file *file, unsigned int cmd,
 	return 0;
 }
 
+static inline int security_memfd_create(char *name, unsigned int flags)
+{
+	return 0;
+}
+
 static inline int security_mmap_file(struct file *file, unsigned long prot,
 				     unsigned long flags)
 {
diff --git a/mm/memfd.c b/mm/memfd.c
index 92f0a5765f7c..f04ed5f0474f 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -356,6 +356,11 @@ SYSCALL_DEFINE2(memfd_create,
 		goto err_name;
 	}
 
+	/* security hook for memfd_create */
+	error = security_memfd_create(name, flags);
+	if (error)
+		return error;
+
 	if (flags & MFD_HUGETLB) {
 		file = hugetlb_file_setup(name, 0, VM_NORESERVE,
 					HUGETLB_ANONHUGE_INODE,
diff --git a/security/security.c b/security/security.c
index 79d82cb6e469..5c018e080923 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1010,6 +1010,19 @@ int security_sb_clone_mnt_opts(const struct super_block *oldsb,
 }
 EXPORT_SYMBOL(security_sb_clone_mnt_opts);
 
+int security_add_mnt_opt(const char *option, const char *val, int len,
+			 void **mnt_opts)
+{
+	return call_int_hook(sb_add_mnt_opt, -EINVAL,
+					option, val, len, mnt_opts);
+}
+EXPORT_SYMBOL(security_add_mnt_opt);
+
+int security_memfd_create(char *name, unsigned int flags)
+{
+	return call_int_hook(memfd_create, 0, name, flags);
+}
+
 int security_move_mount(const struct path *from_path, const struct path *to_path)
 {
 	return call_int_hook(move_mount, 0, from_path, to_path);
-- 
2.39.0.rc0.267.gcb52ba06e7-goog