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SubjectRe: [PATCH] drivers: binderfs: fix memory leak in binderfs_fill_super
On Fri, Aug 12, 2022 at 04:32:28PM +0200, Greg Kroah-Hartman wrote:

> > It's a bit tricky to follow but d_make_root() always consumes the inode.
> > On success via d_instantiate() and on failure via iput(). So when
> > d_make_root() has been called the inode is off limits. And as soon as
> > d_make_root() has returned successfully we're guaranteed that
> > sb->s_fs_info is cleaned up if a ->put_super() method has been defined.
> > Just fyi.
>
> Ah, thanks, that wasn't obvious at all.
>
> greg k-h

FWIW, I would rather provide a proper ->kill_sb() and gotten rid of
all that stuff. The thing is, unlike ->put_super(), ->kill_sb() is
called for *anything* that has gotten to foo_fill_super(). Usually
allows to get rid of those "call all of or parts of foo_put_super()
on failure exits" and associated bitrot...

Like this (completely untested):

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index 588d753a7a19..c760f3129768 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -340,22 +340,21 @@ static int binderfs_show_options(struct seq_file *seq, struct dentry *root)
return 0;
}

-static void binderfs_put_super(struct super_block *sb)
+static void binderfs_kill_super(struct super_block *sb)
{
struct binderfs_info *info = sb->s_fs_info;

+ kill_litter_super(sb);
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)
@@ -789,7 +788,7 @@ 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,
};

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