Re: [PATCH] drivers: binderfs: fix memory leak in binderfs_fill_super

[Christian Brauner]

On Fri, Aug 12, 2022 at 09:21:24PM +0800, Dongliang Mu wrote:
> From: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
> 
> In binderfs_fill_super, if s_root is not successfully initialized by
> d_make_root, the previous allocated s_sb_info will not be freed since
> generic_shutdown_super first checks if sb->s_root and then does
> put_super operation. The put_super operation calls binderfs_put_super
> to deallocate s_sb_info and put ipc_ns. This will lead to memory leak
> in binderfs_fill_super.
> 
> Fix this by invoking binderfs_put_super at error sites before s_root
> is successfully initialized.
> 
> Fixes: 095cf502b31e ("binderfs: port to new mount api")
> Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
> Signed-off-by: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
> ---

Seems right but where's the full syzbot link to the issue?
Also, wouldn't (untested) sm like the below be better?:

diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index 588d753a7a19..4582b043d21e 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -692,6 +692,15 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
        sb->s_magic = BINDERFS_SUPER_MAGIC;
        sb->s_op = &binderfs_super_ops;
        sb->s_time_gran = 1;
+       sb->s_fs_info = NULL;
+
+       inode = new_inode(sb);
+       if (!inode)
+               return -ENOMEM;
+
+       sb->s_root = d_make_root(inode);
+       if (!sb->s_root)
+               return -ENOMEM;

        sb->s_fs_info = kzalloc(sizeof(struct binderfs_info), GFP_KERNEL);
        if (!sb->s_fs_info)
@@ -709,10 +718,6 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
        info->mount_opts.max = ctx->max;
        info->mount_opts.stats_mode = ctx->stats_mode;

-       inode = new_inode(sb);
-       if (!inode)
-               return -ENOMEM;
-
        inode->i_ino = FIRST_INODE;
        inode->i_fop = &simple_dir_operations;
        inode->i_mode = S_IFDIR | 0755;
@@ -720,10 +725,6 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
        inode->i_op = &binderfs_dir_inode_operations;
        set_nlink(inode, 2);

-       sb->s_root = d_make_root(inode);
-       if (!sb->s_root)
-               return -ENOMEM;
-
        ret = binderfs_binder_ctl_create(sb);
        if (ret)
                return ret;

>  drivers/android/binderfs.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
> index 588d753a7a19..20f5bc77495f 100644
> --- a/drivers/android/binderfs.c
> +++ b/drivers/android/binderfs.c
> @@ -710,8 +710,10 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
>  	info->mount_opts.stats_mode = ctx->stats_mode;
>  
>  	inode = new_inode(sb);
> -	if (!inode)
> +	if (!inode) {
> +		binderfs_put_super(sb);
>  		return -ENOMEM;
> +	}
>  
>  	inode->i_ino = FIRST_INODE;
>  	inode->i_fop = &simple_dir_operations;
> @@ -721,8 +723,10 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
>  	set_nlink(inode, 2);
>  
>  	sb->s_root = d_make_root(inode);
> -	if (!sb->s_root)
> +	if (!sb->s_root) {
> +		binderfs_put_super(sb);
>  		return -ENOMEM;
> +	}
>  
>  	ret = binderfs_binder_ctl_create(sb);
>  	if (ret)
> -- 
> 2.25.1
>