binderfs: rework superblock destruction

So far we relied on
.put_super = binderfs_put_super()
to destroy info we stashed in sb->s_fs_info. This gave us the required ordering
between ->evict_inode() and sb->s_fs_info destruction.

But the current implementation of binderfs_fill_super() has a memory leak in
the rare circumstance that d_make_root() fails because ->put_super() is only
called when sb->s_root is initialized. Fix this by removing ->put_super() and
simply do all that work in binderfs_kill_super().

Reported-by: Dongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Link: https://lore.kernel.org/r/20220823095339.853371-1-brauner@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index 44939ea..09b2ce7 100644 (file)
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -339,22 +339,10 @@ static int binderfs_show_options(struct seq_file *seq, struct dentry *root)
        return 0;
 }
 
-static void binderfs_put_super(struct super_block *sb)
-{
-       struct binderfs_info *info = sb->s_fs_info;
-
-       if (info && info->ipc_ns)
-               put_ipc_ns(info->ipc_ns);
-
-       kfree(info);
-       sb->s_fs_info = NULL;
-}
-
 static const struct super_operations binderfs_super_ops = {
        .evict_inode    = binderfs_evict_inode,
        .show_options   = binderfs_show_options,
        .statfs         = simple_statfs,
-       .put_super      = binderfs_put_super,
 };
 
 static inline bool is_binderfs_control_device(const struct dentry *dentry)
@@ -784,11 +772,27 @@ static int binderfs_init_fs_context(struct fs_context *fc)
        return 0;
 }
 
+static void binderfs_kill_super(struct super_block *sb)
+{
+       struct binderfs_info *info = sb->s_fs_info;
+
+       /*
+        * During inode eviction struct binderfs_info is needed.
+        * So first wipe the super_block then free struct binderfs_info.
+        */
+       kill_litter_super(sb);
+
+       if (info && info->ipc_ns)
+               put_ipc_ns(info->ipc_ns);
+
+       kfree(info);
+}
+
 static struct file_system_type binder_fs_type = {
        .name                   = "binder",
        .init_fs_context        = binderfs_init_fs_context,
        .parameters             = binderfs_fs_parameters,
-       .kill_sb                = kill_litter_super,
+       .kill_sb                = binderfs_kill_super,
        .fs_flags               = FS_USERNS_MOUNT,
 };