[PATCH] fs/squashfs: fix reading of fragmented files

[Richard Genoud]

Le 17/05/2021 à 23:20, Joao Marcos Costa a écrit :
> The fragmented files were not correctly read because of two issues:
> 
> - The squashfs_file_info struct has a field named 'comp', which tells if
> the file's fragment is compressed or not. This field was always set to
> 'true' in sqfs_get_regfile_info and sqfs_get_lregfile_info. It should
> actually take sqfs_frag_lookup's return value. This patch addresses
> these two assignments.
> 
> - In sqfs_read, the fragments (compressed or not) were copied to the
> output buffer through a for loop which was reading data at the wrong
> offset. Replace these loops by equivalent calls to memcpy, with the
> right parameters.
> 
> I tested this patch by comparing the MD5 checksum of a few fragmented
> files with the respective md5sum output in sandbox, considering both
> compressed and uncompressed fragments.
> 
> Signed-off-by: Joao Marcos Costa <jmcosta944 at gmail.com>
Tested-by: Richard Genoud <richard.genoud at posteo.net>

Tested it on real hardware, with mksquashfs -always-use-fragments, loading a kernel (fit) from squashfs.
It wasn't working before the patch, and works after.

Thanks !
> ---
>   fs/squashfs/sqfs.c | 16 ++++++----------
>   1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/squashfs/sqfs.c b/fs/squashfs/sqfs.c
> index 29805c3c6f..22ef4f2691 100644
> --- a/fs/squashfs/sqfs.c
> +++ b/fs/squashfs/sqfs.c
> @@ -1253,7 +1253,7 @@ static int sqfs_get_regfile_info(struct squashfs_reg_inode *reg,
>   				       fentry);
>   		if (ret < 0)
>   			return -EINVAL;
> -		finfo->comp = true;
> +		finfo->comp = ret;
>   		if (fentry->size < 1 || fentry->start == 0x7FFFFFFF)
>   			return -EINVAL;
>   	} else {
> @@ -1291,7 +1291,7 @@ static int sqfs_get_lregfile_info(struct squashfs_lreg_inode *lreg,
>   				       fentry);
>   		if (ret < 0)
>   			return -EINVAL;
> -		finfo->comp = true;
> +		finfo->comp = ret;
>   		if (fentry->size < 1 || fentry->start == 0x7FFFFFFF)
>   			return -EINVAL;
>   	} else {
> @@ -1547,20 +1547,16 @@ int sqfs_read(const char *filename, void *buf, loff_t offset, loff_t len,
>   			goto out;
>   		}
>   
> -		for (j = *actread; j < finfo.size; j++) {
> -			memcpy(buf + j, &fragment_block[finfo.offset + j], 1);
> -			(*actread)++;
> -		}
> +		memcpy(buf + *actread, &fragment_block[finfo.offset], finfo.size - *actread);
> +		*actread = finfo.size;
>   
>   		free(fragment_block);
>   
>   	} else if (finfo.frag && !finfo.comp) {
>   		fragment_block = (void *)fragment + table_offset;
>   
> -		for (j = *actread; j < finfo.size; j++) {
> -			memcpy(buf + j, &fragment_block[finfo.offset + j], 1);
> -			(*actread)++;
> -		}
> +		memcpy(buf + *actread, &fragment_block[finfo.offset], finfo.size - *actread);
> +		*actread = finfo.size;
>   	}
>   
>   out:
>