Subject: Re: [PATCH 1/5] cachefiles: Fix __cachefiles_prepare_write()

From: Simon Horman <[email-masked]>
Date: Sun, 7 Jan 2024 16:09:16 +0000

On Wed, Jan 03, 2024 at 02:59:25PM +0000, David Howells wrote:
> Fix __cachefiles_prepare_write() to correctly determine whether the
> requested write will fit correctly with the DIO alignment.
> 
> Reported-by: Gao Xiang <[email-masked]>
> Signed-off-by: David Howells <[email-masked]>
> Tested-by: Yiqun Leng <[email-masked]>
> Tested-by: Jia Zhu <[email-masked]>
> cc: Jeff Layton <[email-masked]>
> cc: [email-masked]
> cc: [email-masked]
> cc: [email-masked]
> cc: [email-masked]
> ---
>  fs/cachefiles/io.c | 28 +++++++++++++++++-----------
>  1 file changed, 17 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
> index bffffedce4a9..7529b40bc95a 100644
> --- a/fs/cachefiles/io.c
> +++ b/fs/cachefiles/io.c
> @@ -522,16 +522,22 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>  			       bool no_space_allocated_yet)
>  {
>  	struct cachefiles_cache *cache = object->volume->cache;
> -	loff_t start = *_start, pos;
> -	size_t len = *_len, down;
> +	unsigned long long start = *_start, pos;
> +	size_t len = *_len;
>  	int ret;
>  
>  	/* Round to DIO size */
> -	down = start - round_down(start, PAGE_SIZE);
> -	*_start = start - down;
> -	*_len = round_up(down + len, PAGE_SIZE);
> -	if (down < start || *_len > upper_len)
> +	start = round_down(*_start, PAGE_SIZE);
> +	if (start != *_start) {
> +		kleave(" = -ENOBUFS [down]");
> +		return -ENOBUFS;
> +	}
> +	if (*_len > upper_len) {
> +		kleave(" = -ENOBUFS [up]");
>  		return -ENOBUFS;
> +	}
> +
> +	*_len = round_up(len, PAGE_SIZE);
>  
>  	/* We need to work out whether there's sufficient disk space to perform
>  	 * the write - but we can skip that check if we have space already
> @@ -542,7 +548,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>  
>  	pos = cachefiles_inject_read_error();
>  	if (pos == 0)
> -		pos = vfs_llseek(file, *_start, SEEK_DATA);
> +		pos = vfs_llseek(file, start, SEEK_DATA);
>  	if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {

Hi David,

I realise these patches have been accepted, but I have a minor nit:
pos is now unsigned, and so cannot be less than zero.

Flagged by Smatch and Coccinelle.

>  		if (pos == -ENXIO)
>  			goto check_space; /* Unallocated tail */
> @@ -550,7 +556,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>  					  cachefiles_trace_seek_error);
>  		return pos;
>  	}
> -	if ((u64)pos >= (u64)*_start + *_len)
> +	if (pos >= start + *_len)
>  		goto check_space; /* Unallocated region */
>  
>  	/* We have a block that's at least partially filled - if we're low on
> @@ -563,13 +569,13 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>  
>  	pos = cachefiles_inject_read_error();
>  	if (pos == 0)
> -		pos = vfs_llseek(file, *_start, SEEK_HOLE);
> +		pos = vfs_llseek(file, start, SEEK_HOLE);
>  	if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {

Ditto.

>  		trace_cachefiles_io_error(object, file_inode(file), pos,
>  					  cachefiles_trace_seek_error);
>  		return pos;
>  	}
> -	if ((u64)pos >= (u64)*_start + *_len)
> +	if (pos >= start + *_len)
>  		return 0; /* Fully allocated */
>  
>  	/* Partially allocated, but insufficient space: cull. */
> @@ -577,7 +583,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>  	ret = cachefiles_inject_remove_error();
>  	if (ret == 0)
>  		ret = vfs_fallocate(file, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> -				    *_start, *_len);
> +				    start, *_len);
>  	if (ret < 0) {
>  		trace_cachefiles_io_error(object, file_inode(file), ret,
>  					  cachefiles_trace_fallocate_error);
>