Re: [RFC PATCH v2 5/9] fs: add anon_inode_getfile_secure() similar to anon_inode_getfd_secure()

Mickaël Salaün
2021-08-12T13:09:50Z

On 11/08/2021 22:48, Paul Moore wrote:
> Extending the secure anonymous inode support to other subsystems
> requires that we have a secure anon_inode_getfile() variant in
> addition to the existing secure anon_inode_getfd() variant.
>
> Thankfully we can reuse the existing __anon_inode_getfile() function
> and just wrap it with the proper arguments.
>
> Signed-off-by: Paul Moore <paul@paul-moore.com>
>
> ---
> v2:
> - no change
> v1:
> - initial draft
> ---
> fs/anon_inodes.c | 29 +++++++++++++++++++++++++++++
> include/linux/anon_inodes.h | 4 ++++
> 2 files changed, 33 insertions(+)
>
> diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
> index a280156138ed..e0c3e33c4177 100644
> --- a/fs/anon_inodes.c
> +++ b/fs/anon_inodes.c
> @@ -148,6 +148,35 @@ struct file *anon_inode_getfile(const char *name,
> }
> EXPORT_SYMBOL_GPL(anon_inode_getfile);
>
> +/**
> + * anon_inode_getfile_secure - Like anon_inode_getfile(), but creates a new
> + * !S_PRIVATE anon inode rather than reuse the
> + * singleton anon inode and calls the
> + * inode_init_security_anon() LSM hook. This
> + * allows for both the inode to have its own
> + * security context and for the LSM to enforce
> + * policy on the inode's creation.
> + *
> + * @name: [in] name of the "class" of the new file
> + * @fops: [in] file operations for the new file
> + * @priv: [in] private data for the new file (will be file's private_data)
> + * @flags: [in] flags
> + * @context_inode:
> + * [in] the logical relationship with the new inode (optional)
> + *
> + * The LSM may use @context_inode in inode_init_security_anon(), but a
> + * reference to it is not held. Returns the newly created file* or an error
> + * pointer. See the anon_inode_getfile() documentation for more information.
> + */
> +struct file *anon_inode_getfile_secure(const char *name,
> + const struct file_operations *fops,
> + void *priv, int flags,
> + const struct inode *context_inode)
> +{
> + return __anon_inode_getfile(name, fops, priv, flags,
> + context_inode, true);

This is not directly related to this patch but why using the "secure"
boolean in __anon_inode_getfile() and __anon_inode_getfd() instead of
checking that context_inode is not NULL? This would simplify the code,
remove this anon_inode_getfile_secure() wrapper and avoid potential
inconsistencies.

> +}
> +
> static int __anon_inode_getfd(const char *name,
> const struct file_operations *fops,
> void *priv, int flags,
> diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
> index 71881a2b6f78..5deaddbd7927 100644
> --- a/include/linux/anon_inodes.h
> +++ b/include/linux/anon_inodes.h
> @@ -15,6 +15,10 @@ struct inode;
> struct file *anon_inode_getfile(const char *name,
> const struct file_operations *fops,
> void *priv, int flags);
> +struct file *anon_inode_getfile_secure(const char *name,
> + const struct file_operations *fops,
> + void *priv, int flags,
> + const struct inode *context_inode);
> int anon_inode_getfd(const char *name, const struct file_operations *fops,
> void *priv, int flags);
> int anon_inode_getfd_secure(const char *name,