[PATCH v2 14/30] acl: use set acl hook

[Christian Brauner]

The current way of setting and getting posix acls through the generic
xattr interface is error prone and type unsafe. The vfs needs to
interpret and fixup posix acls before storing or reporting it to
userspace. Various hacks exist to make this work. The code is hard to
understand and difficult to maintain in it's current form. Instead of
making this work by hacking posix acls through xattr handlers we are
building a dedicated posix acl api around the get and set inode
operations. This removes a lot of hackiness and makes the codepaths
easier to maintain. A lot of background can be found in [1].

So far posix acls were passed as a void blob to the security and
integrity modules. Some of them like evm then proceed to interpret the
void pointer and convert it into the kernel internal struct posix acl
representation to perform their integrity checking magic. This is
obviously pretty problematic as that requires knowledge that only the
vfs is guaranteed to have and has lead to various bugs.

Now that we have a proper security hook for setting posix acls that
passes down the posix acls in their appropriate vfs format instead of
hacking it through a void pointer stored in the uapi format make use of
it in the new posix acl api.

Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1]
Signed-off-by: Christian Brauner (Microsoft) <brauner at kernel.org>
---

Notes:
    /* v2 */
    unchanged

 fs/posix_acl.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index f19ded0978e5..471d17fa1611 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -24,6 +24,7 @@
 #include <linux/user_namespace.h>
 #include <linux/namei.h>
 #include <linux/mnt_idmapping.h>
+#include <linux/security.h>
 #include <linux/fsnotify.h>
 
 static struct posix_acl **acl_by_type(struct inode *inode, int type)
@@ -1336,6 +1337,10 @@ int vfs_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 	if (error)
 		goto out_inode_unlock;
 
+	error = security_inode_set_acl(mnt_userns, dentry, acl_name, kacl);
+	if (error)
+		goto out_inode_unlock;
+
 	error = try_break_deleg(inode, &delegated_inode);
 	if (error)
 		goto out_inode_unlock;
-- 
2.34.1