Fix races around the access to ->s_options

Put generic_show_options read access to s_options under rcu_read_lock,
split save_mount_options() into "we are setting it the first time"
(uses in foo_fill_super()) and "we are relacing and freeing the old one",
synchronize_rcu() before kfree() in the latter.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/afs/super.c b/fs/afs/super.c
index 2753f16dd315..76828e5f8a39 100644
--- a/fs/afs/super.c
+++ b/fs/afs/super.c
@@ -408,17 +408,17 @@ static int afs_get_sb(struct file_system_type *fs_type,
                         deactivate_locked_super(sb);
                         goto error;
                 }
-                sb->s_options = new_opts;
+                save_mount_options(sb, new_opts);
                 sb->s_flags |= MS_ACTIVE;
         } else {
                 _debug("reuse");
-                kfree(new_opts);
                 ASSERTCMP(sb->s_flags, &, MS_ACTIVE);
         }
 
         simple_set_mnt(mnt, sb);
         afs_put_volume(params.volume);
         afs_put_cell(params.cell);
+        kfree(new_opts);
         _leave(" = 0 [%p]", sb);
         return 0;