On 12/08/2021 16:32, Paul Moore wrote:

On Thu, Aug 12, 2021 at 5:32 AM Mickaël Salaün [off-list ref] wrote:

quoted

On 11/08/2021 22:48, Paul Moore wrote:

quoted

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.

The issue is that it is acceptable for the context_inode to be either
valid or NULL for callers who request the "secure" code path.

Look at the SELinux implementation of the anonymous inode hook in
selinux_inode_init_security_anon() and you will see that in cases
where the context_inode is valid we simply inherit the label from the
given inode, whereas if context_inode is NULL we do a type transition
using the requesting task and the anonymous inode's "name".

Indeed.

Acked-by: Mickaël Salaün <redacted>