fsnotify, lsm: Decouple fsnotify from lsm

[PATCH v2] fsnotify, lsm: Decouple fsnotify from lsm

Posted by Song Liu 1 month, 2 weeks ago

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@kernel.org>
Acked-by: Paul Moore <paul@paul-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

Re: [PATCH v2] fsnotify, lsm: Decouple fsnotify from lsm

Posted by Amir Goldstein 1 month, 2 weeks ago

On Sun, Oct 13, 2024 at 2:23 AM Song Liu <song@kernel.org> wrote:
>
> 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.

Maybe I am missing something.
I like cleaner interfaces, but if it is a report of a problem then
I do not understand what the problem is.
IOW, what does "This is not right" mean?

>
> 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@kernel.org>
> Acked-by: Paul Moore <paul@paul-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.

I did not understand why you claim that the tags are or not necessary.
The dependency is due to removal of the fsnotify.h include.

Anyway, I don't think it is critical to backport this fix.
The dependencies would probably fail to apply cleanly to older kernels,
so unless somebody cares, it would stay this way.

>
> Fixes: c4ec54b40d33 ("fsnotify: new fsnotify hooks and events types for access decisions")

Because I am not sure what the problem is, I am not sure that a Fixes:
tag is called for.

> Depends-on: 36e28c42187c ("fsnotify: split fsnotify_perm() into two hooks")
> Depends-on: d9e5d31084b0 ("fsnotify: optionally pass access range in file permission hooks")

These need to be in the commit message in case AUTOSEL or a developer
would decide to backport your change.

Thanks,
Amir.

> ---
>  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
>
>