xattr: use posix acl api

In previous patches we built a new posix api solely around get and set
inode operations. Now that we have all the pieces in place we can switch
the system calls and the vfs over to only rely on this api when
interacting with posix acls. This finally removes all type unsafety and
type conversion issues explained in detail in [1] that we aim to get rid
of.

With the new posix acl api we immediately translate into an appropriate
kernel internal struct posix_acl format both when getting and setting
posix acls. This is a stark contrast to before were we hacked unsafe raw
values into the uapi struct that was stored in a void pointer relying
and having filesystems and security modules hack around in the uapi
struct as well.

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

3 files changed, 77 insertions, 11 deletions

diff --git a/fs/internal.h b/fs/internal.h
index aa5f240496d9..e377eb7bbe7f 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -234,4 +234,24 @@ int do_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 		struct xattr_ctx *ctx);
 int may_write_xattr(struct user_namespace *mnt_userns, struct inode *inode);
 
+#ifdef CONFIG_FS_POSIX_ACL
+int do_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
+	       const char *acl_name, const void *kvalue, size_t size);
+ssize_t do_get_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
+		   const char *acl_name, void *kvalue, size_t size);
+#else
+static inline int do_set_acl(struct user_namespace *mnt_userns,
+			     struct dentry *dentry, const char *acl_name,
+			     const void *kvalue, size_t size)
+{
+	return -EOPNOTSUPP;
+}
+static inline ssize_t do_get_acl(struct user_namespace *mnt_userns,
+				 struct dentry *dentry, const char *acl_name,
+				 void *kvalue, size_t size)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
 ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *pos);
diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 3a141082b24c..14b87653b797 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -1544,3 +1544,40 @@ out_inode_unlock:
 	return error;
 }
 EXPORT_SYMBOL_GPL(vfs_remove_acl);
+
+int do_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
+	       const char *acl_name, const void *kvalue, size_t size)
+{
+	int error;
+	struct posix_acl *acl = NULL;
+
+	if (size) {
+		/*
+		 * Note that posix_acl_from_xattr() uses GFP_NOFS when it
+		 * probably doesn't need to here.
+		 */
+		acl = posix_acl_from_xattr(current_user_ns(), kvalue, size);
+		if (IS_ERR(acl))
+			return PTR_ERR(acl);
+	}
+
+	error = vfs_set_acl(mnt_userns, dentry, acl_name, acl);
+	posix_acl_release(acl);
+	return error;
+}
+
+ssize_t do_get_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
+		   const char *acl_name, void *kvalue, size_t size)
+{
+	ssize_t error;
+	struct posix_acl *acl;
+
+	acl = vfs_get_acl(mnt_userns, dentry, acl_name);
+	if (IS_ERR(acl))
+		return PTR_ERR(acl);
+
+	error = vfs_posix_acl_to_xattr(mnt_userns, d_inode(dentry),
+				       acl, kvalue, size);
+	posix_acl_release(acl);
+	return error;
+}
diff --git a/fs/xattr.c b/fs/xattr.c
index 9ed9eea4d1b9..77db5aa26d13 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -189,6 +189,9 @@ __vfs_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 {
 	const struct xattr_handler *handler;
 
+	if (is_posix_acl_xattr(name))
+		return -EOPNOTSUPP;
+
 	handler = xattr_resolve_name(inode, &name);
 	if (IS_ERR(handler))
 		return PTR_ERR(handler);
@@ -410,6 +413,9 @@ __vfs_getxattr(struct dentry *dentry, struct inode *inode, const char *name,
 {
 	const struct xattr_handler *handler;
 
+	if (is_posix_acl_xattr(name))
+		return -EOPNOTSUPP;
+
 	handler = xattr_resolve_name(inode, &name);
 	if (IS_ERR(handler))
 		return PTR_ERR(handler);
@@ -482,6 +488,9 @@ __vfs_removexattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 	struct inode *inode = d_inode(dentry);
 	const struct xattr_handler *handler;
 
+	if (is_posix_acl_xattr(name))
+		return -EOPNOTSUPP;
+
 	handler = xattr_resolve_name(inode, &name);
 	if (IS_ERR(handler))
 		return PTR_ERR(handler);
@@ -591,17 +600,13 @@ int setxattr_copy(const char __user *name, struct xattr_ctx *ctx)
 	return error;
 }
 
-static void setxattr_convert(struct user_namespace *mnt_userns,
-			     struct dentry *d, struct xattr_ctx *ctx)
-{
-	if (ctx->size && is_posix_acl_xattr(ctx->kname->name))
-		posix_acl_fix_xattr_from_user(ctx->kvalue, ctx->size);
-}
-
 int do_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 		struct xattr_ctx *ctx)
 {
-	setxattr_convert(mnt_userns, dentry, ctx);
+	if (is_posix_acl_xattr(ctx->kname->name))
+		return do_set_acl(mnt_userns, dentry, ctx->kname->name,
+				  ctx->kvalue, ctx->size);
+
 	return vfs_setxattr(mnt_userns, dentry, ctx->kname->name,
 			ctx->kvalue, ctx->size, ctx->flags);
 }
@@ -708,10 +713,11 @@ do_getxattr(struct user_namespace *mnt_userns, struct dentry *d,
 			return -ENOMEM;
 	}
 
-	error = vfs_getxattr(mnt_userns, d, kname, ctx->kvalue, ctx->size);
+	if (is_posix_acl_xattr(ctx->kname->name))
+		error = do_get_acl(mnt_userns, d, kname, ctx->kvalue, ctx->size);
+	else
+		error = vfs_getxattr(mnt_userns, d, kname, ctx->kvalue, ctx->size);
 	if (error > 0) {
-		if (is_posix_acl_xattr(kname))
-			posix_acl_fix_xattr_to_user(ctx->kvalue, error);
 		if (ctx->size && copy_to_user(ctx->value, ctx->kvalue, error))
 			error = -EFAULT;
 	} else if (error == -ERANGE && ctx->size >= XATTR_SIZE_MAX) {
@@ -886,6 +892,9 @@ removexattr(struct user_namespace *mnt_userns, struct dentry *d,
 	if (error < 0)
 		return error;
 
+	if (is_posix_acl_xattr(kname))
+		return vfs_remove_acl(mnt_userns, d, kname);
+
 	return vfs_removexattr(mnt_userns, d, kname);
 }