linux-kernel - Re: [PATCH] ubifs: Free memory for tmpfile name

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Date:   Thu, 30 Mar 2023 10:25:59 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     Mårten Lindahl <marten.lindahl@...s.com>,
        Richard Weinberger <richard@....at>
CC:     <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <kernel@...s.com>
Subject: Re: [PATCH] ubifs: Free memory for tmpfile name

Hi Mårten,
> When opening a ubifs tmpfile on an encrypted directory, function
> fscrypt_setup_filename allocates memory for the name that is to be
> stored in the directory entry, but after the name has been copied to the
> directory entry inode, the memory is not freed.
> 
> When running kmemleak on it we see that it is registered as a leak. The
> report below is triggered by a simple program 'tmpfile' just opening a
> tmpfile:
> 
>    unreferenced object 0xffff88810178f380 (size 32):
>      comm "tmpfile", pid 509, jiffies 4294934744 (age 1524.742s)
>      backtrace:
>        __kmem_cache_alloc_node
>        __kmalloc
>        fscrypt_setup_filename
>        ubifs_tmpfile
>        vfs_tmpfile
>        path_openat
> 
> Free this memory after it has been copied to the inode.
> 
> Signed-off-by: Mårten Lindahl <marten.lindahl@...s.com>
> ---
>   fs/ubifs/dir.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
> index 0f29cf201136..089ca6910124 100644
> --- a/fs/ubifs/dir.c
> +++ b/fs/ubifs/dir.c
> @@ -491,6 +491,7 @@ static int ubifs_tmpfile(struct user_namespace *mnt_userns, struct inode *dir,
>   		goto out_cancel;
>   	unlock_2_inodes(dir, inode);
>   
> +	fscrypt_free_filename(&nm);
>   	ubifs_release_budget(c, &req);
>   
>   	return finish_open_simple(file, 0);

Looks good, just one small nit. I'd prefer to add 
fscrypt_free_filename() after ubifs_release_budget() just like 
ubifs_create/link does, so that ubifs can get unused budget earlier.

After looking through the code, I found another place create_whiteout 
has the same problem(Imported in 278d9a243635f26c05("ubifs: Rename 
whiteout atomically") by me). Would you mind fixing this point just by 
removing unused 'nm' in create_whiteout()?

> 
> ---
> base-commit: c9c3395d5e3dcc6daee66c6908354d47bf98cb0c
> change-id: 20230329-memleak-fix-87a01daf469e
> 
> Best regards,
>