[U-Boot,v5,2/8] ext4: recover from filesystem corruption when reading

From: Ian Ray <ian.ray@ge.com>

Some fixes when reading EXT files and directory entries were identified
after using e2fuzz to corrupt an EXT3 filesystem:

 - Stop reading directory entries if the offset becomes badly aligned.

 - Avoid overwriting memory by clamping the length used to zero the buffer
   in ext4fs_read_file.  Also sanity check blocksize.

Signed-off-by: Ian Ray <ian.ray@ge.com>
Signed-off-by: Martyn Welch <martyn.welch@collabora.co.uk>
---
 fs/ext4/ext4_common.c | 10 ++++++++++
 fs/ext4/ext4fs.c      | 10 +++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

On 08/11/2017 16:35, Martyn Welch wrote:
> From: Ian Ray <ian.ray@ge.com>
> 
> Some fixes when reading EXT files and directory entries were identified
> after using e2fuzz to corrupt an EXT3 filesystem:
> 
>  - Stop reading directory entries if the offset becomes badly aligned.
> 
>  - Avoid overwriting memory by clamping the length used to zero the buffer
>    in ext4fs_read_file.  Also sanity check blocksize.
> 
> Signed-off-by: Ian Ray <ian.ray@ge.com>
> Signed-off-by: Martyn Welch <martyn.welch@collabora.co.uk>
> ---
>  fs/ext4/ext4_common.c | 10 ++++++++++
>  fs/ext4/ext4fs.c      | 10 +++++++++-
>  2 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
> index 31952f4..dac9545 100644
> --- a/fs/ext4/ext4_common.c
> +++ b/fs/ext4/ext4_common.c
> @@ -660,6 +660,11 @@ static int search_dir(struct ext2_inode *parent_inode, char *dirname)
>  
>  		offset = 0;
>  		do {
> +			if (offset & 3) {
> +				printf("Badly aligned ext2_dirent\n");
> +				break;
> +			}
> +
>  			dir = (struct ext2_dirent *)(block_buffer + offset);
>  			direntname = (char*)(dir) + sizeof(struct ext2_dirent);
>  
> @@ -880,6 +885,11 @@ static int unlink_filename(char *filename, unsigned int blknr)
>  
>  	offset = 0;
>  	do {
> +		if (offset & 3) {
> +			printf("Badly aligned ext2_dirent\n");
> +			break;
> +		}
> +
>  		previous_dir = dir;
>  		dir = (struct ext2_dirent *)(block_buffer + offset);
>  		direntname = (char *)(dir) + sizeof(struct ext2_dirent);
> diff --git a/fs/ext4/ext4fs.c b/fs/ext4/ext4fs.c
> index b0c7303..9ee2caf 100644
> --- a/fs/ext4/ext4fs.c
> +++ b/fs/ext4/ext4fs.c
> @@ -64,6 +64,9 @@ int ext4fs_read_file(struct ext2fs_node *node, loff_t pos,
>  	char *delayed_buf = NULL;
>  	short status;
>  
> +	if (blocksize <= 0)
> +		return -1;
> +
>  	/* Adjust len so it we can't read past the end of the file. */
>  	if (len + pos > filesize)
>  		len = (filesize - pos);
> @@ -127,6 +130,7 @@ int ext4fs_read_file(struct ext2fs_node *node, loff_t pos,
>  					(blockend >> log2blksz);
>  			}
>  		} else {
> +			int n;
>  			if (previous_block_number != -1) {
>  				/* spill */
>  				status = ext4fs_devread(delayed_start,
> @@ -137,7 +141,11 @@ int ext4fs_read_file(struct ext2fs_node *node, loff_t pos,
>  					return -1;
>  				previous_block_number = -1;
>  			}
> -			memset(buf, 0, blocksize - skipfirst);
> +			/* Zero no more than `len' bytes. */
> +			n = blocksize - skipfirst;
> +			if (n > len)
> +				n = len;
> +			memset(buf, 0, n);
>  		}
>  		buf += blocksize - skipfirst;
>  	}
> 

Reviewed-by: Stefano Babic <sbabic@denx.de>

Best regards,
Stefano Babic