[PATCH] ecryptfs: avoid heap allocation for inode size write

[PATCH] ecryptfs: avoid heap allocation for inode size write

[Yichong Chen]

ecryptfs_write_inode_size_to_header() allocates an 8-byte buffer only
to write the encoded inode size to the lower file header.

Use a stack __be64 value instead. This avoids an unnecessary allocation
and removes a failure path without changing the data written to disk.

Signed-off-by: Yichong Chen <chenyichong@uniontech.com>
---
 fs/ecryptfs/mmap.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index 2c2b12fedeae..0222f98143ab 100644
--- a/fs/ecryptfs/mmap.c
+++ b/fs/ecryptfs/mmap.c
@@ -355,24 +355,17 @@ static int ecryptfs_write_begin(const struct kiocb *iocb,
  */
 static int ecryptfs_write_inode_size_to_header(struct inode *ecryptfs_inode)
 {
-	char *file_size_virt;
+	__be64 file_size;
 	int rc;
 
-	file_size_virt = kmalloc(sizeof(u64), GFP_KERNEL);
-	if (!file_size_virt) {
-		rc = -ENOMEM;
-		goto out;
-	}
-	put_unaligned_be64(i_size_read(ecryptfs_inode), file_size_virt);
-	rc = ecryptfs_write_lower(ecryptfs_inode, file_size_virt, 0,
-				  sizeof(u64));
-	kfree(file_size_virt);
+	file_size = cpu_to_be64(i_size_read(ecryptfs_inode));
+	rc = ecryptfs_write_lower(ecryptfs_inode, (char *)&file_size, 0,
+				  sizeof(file_size));
 	if (rc < 0)
 		printk(KERN_ERR "%s: Error writing file size to header; "
 		       "rc = [%d]\n", __func__, rc);
 	else
 		rc = 0;
-out:
 	return rc;
 }
 
-- 
2.51.0

Re: [PATCH] ecryptfs: avoid heap allocation for inode size write

[Tyler Hicks]

On 2026-06-30 11:08:00, Yichong Chen wrote:
> ecryptfs_write_inode_size_to_header() allocates an 8-byte buffer only
> to write the encoded inode size to the lower file header.
> 
> Use a stack __be64 value instead. This avoids an unnecessary allocation
> and removes a failure path without changing the data written to disk.
> 
> Signed-off-by: Yichong Chen <chenyichong@uniontech.com>

This is much better. Thanks for the improvement!

I'll put your patches through some testing and then respond when they've
been applied. Thanks!

Tyler

> ---
>  fs/ecryptfs/mmap.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
> index 2c2b12fedeae..0222f98143ab 100644
> --- a/fs/ecryptfs/mmap.c
> +++ b/fs/ecryptfs/mmap.c
> @@ -355,24 +355,17 @@ static int ecryptfs_write_begin(const struct kiocb *iocb,
>   */
>  static int ecryptfs_write_inode_size_to_header(struct inode *ecryptfs_inode)
>  {
> -	char *file_size_virt;
> +	__be64 file_size;
>  	int rc;
>  
> -	file_size_virt = kmalloc(sizeof(u64), GFP_KERNEL);
> -	if (!file_size_virt) {
> -		rc = -ENOMEM;
> -		goto out;
> -	}
> -	put_unaligned_be64(i_size_read(ecryptfs_inode), file_size_virt);
> -	rc = ecryptfs_write_lower(ecryptfs_inode, file_size_virt, 0,
> -				  sizeof(u64));
> -	kfree(file_size_virt);
> +	file_size = cpu_to_be64(i_size_read(ecryptfs_inode));
> +	rc = ecryptfs_write_lower(ecryptfs_inode, (char *)&file_size, 0,
> +				  sizeof(file_size));
>  	if (rc < 0)
>  		printk(KERN_ERR "%s: Error writing file size to header; "
>  		       "rc = [%d]\n", __func__, rc);
>  	else
>  		rc = 0;
> -out:
>  	return rc;
>  }
>  
> -- 
> 2.51.0
>