xattr: handle idmapped mounts

When interacting with extended attributes the vfs verifies that the
caller is privileged over the inode with which the extended attribute is
associated. For posix access and posix default extended attributes a uid
or gid can be stored on-disk. Let the functions handle posix extended
attributes on idmapped mounts. If the inode is accessed through an
idmapped mount we need to map it according to the mount's user
namespace. Afterwards the checks are identical to non-idmapped mounts.
This has no effect for e.g. security xattrs since they don't store uids
or gids and don't perform permission checks on them like posix acls do.

Link: https://lore.kernel.org/r/20210121131959.646623-10-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: Tycho Andersen <tycho@tycho.pizza>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

1 files changed, 14 insertions, 15 deletions

diff --git a/fs/cachefiles/xattr.c b/fs/cachefiles/xattr.c
index 72e42438f3d7..a591b5e09637 100644
--- a/fs/cachefiles/xattr.c
+++ b/fs/cachefiles/xattr.c
@@ -39,8 +39,8 @@ int cachefiles_check_object_type(struct cachefiles_object *object)
 	_enter("%p{%s}", object, type);
 
 	/* attempt to install a type label directly */
-	ret = vfs_setxattr(dentry, cachefiles_xattr_cache, type, 2,
-			   XATTR_CREATE);
+	ret = vfs_setxattr(&init_user_ns, dentry, cachefiles_xattr_cache, type,
+			   2, XATTR_CREATE);
 	if (ret == 0) {
 		_debug("SET"); /* we succeeded */
 		goto error;
@@ -54,7 +54,8 @@ int cachefiles_check_object_type(struct cachefiles_object *object)
 	}
 
 	/* read the current type label */
-	ret = vfs_getxattr(dentry, cachefiles_xattr_cache, xtype, 3);
+	ret = vfs_getxattr(&init_user_ns, dentry, cachefiles_xattr_cache, xtype,
+			   3);
 	if (ret < 0) {
 		if (ret == -ERANGE)
 			goto bad_type_length;
@@ -110,9 +111,8 @@ int cachefiles_set_object_xattr(struct cachefiles_object *object,
 	_debug("SET #%u", auxdata->len);
 
 	clear_bit(FSCACHE_COOKIE_AUX_UPDATED, &object->fscache.cookie->flags);
-	ret = vfs_setxattr(dentry, cachefiles_xattr_cache,
-			   &auxdata->type, auxdata->len,
-			   XATTR_CREATE);
+	ret = vfs_setxattr(&init_user_ns, dentry, cachefiles_xattr_cache,
+			   &auxdata->type, auxdata->len, XATTR_CREATE);
 	if (ret < 0 && ret != -ENOMEM)
 		cachefiles_io_error_obj(
 			object,
@@ -140,9 +140,8 @@ int cachefiles_update_object_xattr(struct cachefiles_object *object,
 	_debug("SET #%u", auxdata->len);
 
 	clear_bit(FSCACHE_COOKIE_AUX_UPDATED, &object->fscache.cookie->flags);
-	ret = vfs_setxattr(dentry, cachefiles_xattr_cache,
-			   &auxdata->type, auxdata->len,
-			   XATTR_REPLACE);
+	ret = vfs_setxattr(&init_user_ns, dentry, cachefiles_xattr_cache,
+			   &auxdata->type, auxdata->len, XATTR_REPLACE);
 	if (ret < 0 && ret != -ENOMEM)
 		cachefiles_io_error_obj(
 			object,
@@ -171,7 +170,7 @@ int cachefiles_check_auxdata(struct cachefiles_object *object)
 	if (!auxbuf)
 		return -ENOMEM;
 
-	xlen = vfs_getxattr(dentry, cachefiles_xattr_cache,
+	xlen = vfs_getxattr(&init_user_ns, dentry, cachefiles_xattr_cache,
 			    &auxbuf->type, 512 + 1);
 	ret = -ESTALE;
 	if (xlen < 1 ||
@@ -213,7 +212,7 @@ int cachefiles_check_object_xattr(struct cachefiles_object *object,
 	}
 
 	/* read the current type label */
-	ret = vfs_getxattr(dentry, cachefiles_xattr_cache,
+	ret = vfs_getxattr(&init_user_ns, dentry, cachefiles_xattr_cache,
 			   &auxbuf->type, 512 + 1);
 	if (ret < 0) {
 		if (ret == -ENODATA)
@@ -270,9 +269,9 @@ int cachefiles_check_object_xattr(struct cachefiles_object *object,
 		}
 
 		/* update the current label */
-		ret = vfs_setxattr(dentry, cachefiles_xattr_cache,
-				   &auxdata->type, auxdata->len,
-				   XATTR_REPLACE);
+		ret = vfs_setxattr(&init_user_ns, dentry,
+				   cachefiles_xattr_cache, &auxdata->type,
+				   auxdata->len, XATTR_REPLACE);
 		if (ret < 0) {
 			cachefiles_io_error_obj(object,
 						"Can't update xattr on %lu"
@@ -309,7 +308,7 @@ int cachefiles_remove_object_xattr(struct cachefiles_cache *cache,
 {
 	int ret;
 
-	ret = vfs_removexattr(dentry, cachefiles_xattr_cache);
+	ret = vfs_removexattr(&init_user_ns, dentry, cachefiles_xattr_cache);
 	if (ret < 0) {
 		if (ret == -ENOENT || ret == -ENODATA)
 			ret = 0;