[v2] selinux: hooks: use kmalloc() to allocate path buffer

[PATCH v2] selinux: hooks: use kmalloc() to allocate path buffer

Posted by Mike Rapoport 1 week ago

From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>

selinux_genfs_get_sid() allocates memory for a path with __get_free_page().

Such usage does not require a "page" and the size of the buffer should
actually be PATH_MAX which may be less than PAGE_SIZE on some
architectures.

Replace __get_free_page() for allocation of a path buffer with kmalloc()
and make it explicit that the buffer size is PATH_MAX.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
v2 changes:
* explicitly use kmalloc() with PATH_MAX

 security/selinux/hooks.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 0f704380a8c8..19493198ece1 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1336,11 +1336,11 @@ static int selinux_genfs_get_sid(struct dentry *dentry,
 	struct super_block *sb = dentry->d_sb;
 	char *buffer, *path;
 
-	buffer = (char *)__get_free_page(GFP_KERNEL);
+	buffer = kmalloc(GFP_KERNEL, PATH_MAX);
 	if (!buffer)
 		return -ENOMEM;
 
-	path = dentry_path_raw(dentry, buffer, PAGE_SIZE);
+	path = dentry_path_raw(dentry, buffer, PATH_MAX);
 	if (IS_ERR(path))
 		rc = PTR_ERR(path);
 	else {
@@ -1361,7 +1361,7 @@ static int selinux_genfs_get_sid(struct dentry *dentry,
 			rc = 0;
 		}
 	}
-	free_page((unsigned long)buffer);
+	kfree(buffer);
 	return rc;
 }
 
-- 
2.53.0

Re: [PATCH v2] selinux: hooks: use kmalloc() to allocate path buffer

Posted by David Laight 1 week ago

On Sun, 31 May 2026 18:15:02 +0300
Mike Rapoport <rppt@kernel.org> wrote:

> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> selinux_genfs_get_sid() allocates memory for a path with __get_free_page().
> 
> Such usage does not require a "page" and the size of the buffer should
> actually be PATH_MAX which may be less than PAGE_SIZE on some
> architectures.
> 
> Replace __get_free_page() for allocation of a path buffer with kmalloc()
> and make it explicit that the buffer size is PATH_MAX.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> v2 changes:
> * explicitly use kmalloc() with PATH_MAX
> 
>  security/selinux/hooks.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 0f704380a8c8..19493198ece1 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -1336,11 +1336,11 @@ static int selinux_genfs_get_sid(struct dentry *dentry,
>  	struct super_block *sb = dentry->d_sb;
>  	char *buffer, *path;
>  
> -	buffer = (char *)__get_free_page(GFP_KERNEL);
> +	buffer = kmalloc(GFP_KERNEL, PATH_MAX);

At least get the args in the right order.

>  	if (!buffer)
>  		return -ENOMEM;
>  
> -	path = dentry_path_raw(dentry, buffer, PAGE_SIZE);
> +	path = dentry_path_raw(dentry, buffer, PATH_MAX);
>  	if (IS_ERR(path))
>  		rc = PTR_ERR(path);
>  	else {
> @@ -1361,7 +1361,7 @@ static int selinux_genfs_get_sid(struct dentry *dentry,
>  			rc = 0;
>  		}
>  	}
> -	free_page((unsigned long)buffer);
> +	kfree(buffer);
>  	return rc;
>  }
>

Re: [PATCH v2] selinux: hooks: use kmalloc() to allocate path buffer

Posted by Mike Rapoport 1 week ago

On Sun, May 31, 2026 at 05:18:11PM +0100, David Laight wrote:
> On Sun, 31 May 2026 18:15:02 +0300
> Mike Rapoport <rppt@kernel.org> wrote:
> 
> > From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> > 
> > selinux_genfs_get_sid() allocates memory for a path with __get_free_page().
> > 
> > Such usage does not require a "page" and the size of the buffer should
> > actually be PATH_MAX which may be less than PAGE_SIZE on some
> > architectures.
> > 
> > Replace __get_free_page() for allocation of a path buffer with kmalloc()
> > and make it explicit that the buffer size is PATH_MAX.
> > 
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> > ---
> > v2 changes:
> > * explicitly use kmalloc() with PATH_MAX
> > 
> >  security/selinux/hooks.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index 0f704380a8c8..19493198ece1 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -1336,11 +1336,11 @@ static int selinux_genfs_get_sid(struct dentry *dentry,
> >  	struct super_block *sb = dentry->d_sb;
> >  	char *buffer, *path;
> >  
> > -	buffer = (char *)__get_free_page(GFP_KERNEL);
> > +	buffer = kmalloc(GFP_KERNEL, PATH_MAX);
> 
> At least get the args in the right order.

oops
 

-- 
Sincerely yours,
Mike.