Commit 786534b92f3c introduced a regression that caused listxattr to
return the POSIX ACL attribute names even though sysfs doesn't support
POSIX ACLs.  This happens because simple_xattr_list checks for NULL
i_acl / i_default_acl, but inode_init_always initializes those fields to
ACL_NOT_CACHED ((void *)-1).  For example:

    $ getfattr -m- -d /sys
    /sys: system.posix_acl_access: Operation not supported
    /sys: system.posix_acl_default: Operation not supported

Fix this in simple_xattr_list by checking if the filesystem supports
POSIX ACLs.

Fixes: 786534b92f3c ("tmpfs: listxattr should include POSIX ACL xattrs")
Reported-by: Marc Aurele La France <t...@tuyoix.net>
Tested-by: Marc Aurèle La France <t...@tuyoix.net>
Signed-off-by: Andreas Gruenbacher <agrue...@redhat.com>
CC: Stable <sta...@vger.kernel.org> # v4.5+
---
 fs/xattr.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index daa732550088..0d6a6a4af861 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -948,17 +948,19 @@ ssize_t simple_xattr_list(struct inode *inode, struct 
simple_xattrs *xattrs,
        int err = 0;
 
 #ifdef CONFIG_FS_POSIX_ACL
-       if (inode->i_acl) {
-               err = xattr_list_one(&buffer, &remaining_size,
-                                    XATTR_NAME_POSIX_ACL_ACCESS);
-               if (err)
-                       return err;
-       }
-       if (inode->i_default_acl) {
-               err = xattr_list_one(&buffer, &remaining_size,
-                                    XATTR_NAME_POSIX_ACL_DEFAULT);
-               if (err)
-                       return err;
+       if (IS_POSIXACL(inode)) {
+               if (inode->i_acl) {
+                       err = xattr_list_one(&buffer, &remaining_size,
+                                            XATTR_NAME_POSIX_ACL_ACCESS);
+                       if (err)
+                               return err;
+               }
+               if (inode->i_default_acl) {
+                       err = xattr_list_one(&buffer, &remaining_size,
+                                            XATTR_NAME_POSIX_ACL_DEFAULT);
+                       if (err)
+                               return err;
+               }
        }
 #endif
 
-- 
2.17.1

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