On Fri, Dec 01, 2023 at 06:09:36PM +0100, Christian Brauner wrote:

On Wed, Nov 29, 2023 at 03:50:26PM -0600, Seth Forshee (DigitalOcean) wrote:

quoted

Provide a type-safe interface for retrieving filesystem capabilities and
a generic implementation suitable for most filesystems. Also add an
internal interface, __vfs_get_fscaps(), which skips security checks for
later use from the capability code.

Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
---
 fs/xattr.c         | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |  4 ++++
 2 files changed, 70 insertions(+)

diff --git a/fs/xattr.c b/fs/xattr.c
index 09d927603433..3abaf9bef0a5 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c

@@ -181,6 +181,72 @@ xattr_supports_user_prefix(struct inode *inode)
 }
 EXPORT_SYMBOL(xattr_supports_user_prefix);
 
+static int generic_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
+			      struct vfs_caps *caps)
+{
+	struct inode *inode = d_inode(dentry);
+	struct vfs_ns_cap_data *nscaps = NULL;
+	int ret;
+
+	ret = (int)vfs_getxattr_alloc(idmap, dentry, XATTR_NAME_CAPS,

I don't think you need that case here.

Yep. I played with a few different implementations of this function, so
I'm guessing I did need it at one point and failed to notice when it was
no longer needed.

quoted

+				      (char **)&nscaps, 0, GFP_NOFS);
+
+	if (ret >= 0)
+		ret = vfs_caps_from_xattr(idmap, i_user_ns(inode), caps, nscaps, ret);
+
+	kfree(nscaps);
+	return ret;
+}
+
+/**
+ * __vfs_get_fscaps - get filesystem capabilities without security checks
+ * @idmap: idmap of the mount the inode was found from
+ * @dentry: the dentry from which to get filesystem capabilities
+ * @caps: storage in which to return the filesystem capabilities
+ *
+ * This function gets the filesystem capabilities for the dentry and returns
+ * them in @caps. It does not perform security checks.
+ *
+ * Return: 0 on success, a negative errno on error.
+ */
+int __vfs_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
+		     struct vfs_caps *caps)

I would rename that to vfs_get_fscaps_nosec(). We do that for
vfs_getxattr_nosec() as well. It's not pretty but it's better than just
slapping underscores onto it imo.

Will do.