linux-kernel - [PATCH v2] fsnotify, lsm: Decouple fsnotify from lsm

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Message-ID: <20241013002248.3984442-1-song@kernel.org>
Date: Sat, 12 Oct 2024 17:22:48 -0700
From: Song Liu <song@...nel.org>
To: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Cc: viro@...iv.linux.org.uk,
	brauner@...nel.org,
	jack@...e.cz,
	paul@...l-moore.com,
	jmorris@...ei.org,
	serge@...lyn.com,
	kernel-team@...com,
	song@...nel.org
Subject: [PATCH v2] fsnotify, lsm: Decouple fsnotify from lsm

Currently, fsnotify_open_perm() is called from security_file_open(). This
is not right for CONFIG_SECURITY=n and CONFIG_FSNOTIFY=y case, as
security_file_open() in this combination will be a no-op and not call
fsnotify_open_perm(). Fix this by calling fsnotify_open_perm() directly.

After this, CONFIG_FANOTIFY_ACCESS_PERMISSIONS does not require
CONFIG_SECURITY any more. Remove the dependency in the config.

Signed-off-by: Song Liu <song@...nel.org>
Acked-by: Paul Moore <paul@...l-moore.com>

---

v1: https://lore.kernel.org/linux-fsdevel/20241011203722.3749850-1-song@kernel.org/

As far as I can tell, it is necessary to back port this to stable. Because
CONFIG_FANOTIFY_ACCESS_PERMISSIONS is the only user of fsnotify_open_perm,
and CONFIG_FANOTIFY_ACCESS_PERMISSIONS depends on CONFIG_SECURITY.
Therefore, the following tags are not necessary. But I include here as
these are discussed in v1.

Fixes: c4ec54b40d33 ("fsnotify: new fsnotify hooks and events types for access decisions")
Depends-on: 36e28c42187c ("fsnotify: split fsnotify_perm() into two hooks")
Depends-on: d9e5d31084b0 ("fsnotify: optionally pass access range in file permission hooks")
---
 fs/notify/fanotify/Kconfig | 1 -
 fs/open.c                  | 4 ++++
 security/security.c        | 9 +--------
 3 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/fs/notify/fanotify/Kconfig b/fs/notify/fanotify/Kconfig
index a511f9d8677b..0e36aaf379b7 100644
--- a/fs/notify/fanotify/Kconfig
+++ b/fs/notify/fanotify/Kconfig
@@ -15,7 +15,6 @@ config FANOTIFY
 config FANOTIFY_ACCESS_PERMISSIONS
 	bool "fanotify permissions checking"
 	depends on FANOTIFY
-	depends on SECURITY
 	default n
 	help
 	   Say Y here is you want fanotify listeners to be able to make permissions
diff --git a/fs/open.c b/fs/open.c
index acaeb3e25c88..6c4950f19cfb 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -946,6 +946,10 @@ static int do_dentry_open(struct file *f,
 	if (error)
 		goto cleanup_all;
 
+	error = fsnotify_open_perm(f);
+	if (error)
+		goto cleanup_all;
+
 	error = break_lease(file_inode(f), f->f_flags);
 	if (error)
 		goto cleanup_all;
diff --git a/security/security.c b/security/security.c
index 6875eb4a59fc..a72cc62c0a07 100644
--- a/security/security.c
+++ b/security/security.c
@@ -19,7 +19,6 @@
 #include <linux/kernel.h>
 #include <linux/kernel_read_file.h>
 #include <linux/lsm_hooks.h>
-#include <linux/fsnotify.h>
 #include <linux/mman.h>
 #include <linux/mount.h>
 #include <linux/personality.h>
@@ -3102,13 +3101,7 @@ int security_file_receive(struct file *file)
  */
 int security_file_open(struct file *file)
 {
-	int ret;
-
-	ret = call_int_hook(file_open, file);
-	if (ret)
-		return ret;
-
-	return fsnotify_open_perm(file);
+	return call_int_hook(file_open, file);
 }
 
 /**
-- 
2.43.5