[PATCH master] fs: ext4: fix bogus behavior on failure to read ext4 block

[Sascha Hauer]

On Wed, Mar 24, 2021 at 01:19:28PM +0100, Ahmad Fatoum wrote:
> The conversion of blknr from a signed 32-bit to an unsigned 64-type resulted
> in the check for error to never return true. Fix this.
> 
> Affected configuration would behave incorrectly when served with invalid
> blocks. Instead of aborting and having the filesystem bubble up an error
> code, it would return invalid data. As there is no ext4 write support,
> this wouldn't lead to ext4 data corruption however.
> 
> Reported-by: Bastian Krause <bst at pengutronix.de>
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
> ---
>  fs/ext4/ext4fs.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)

Applied, thanks

Sascha

> 
> diff --git a/fs/ext4/ext4fs.c b/fs/ext4/ext4fs.c
> index 54349aad3f3f..344d423fd9c4 100644
> --- a/fs/ext4/ext4fs.c
> +++ b/fs/ext4/ext4fs.c
> @@ -74,11 +74,11 @@ loff_t ext4fs_read_file(struct ext2fs_node *node, loff_t pos,
>  		loff_t blockend = blocksize;
>  		loff_t skipfirst = 0;
>  
> -		blknr = read_allocated_block(node, i);
> -		if (blknr < 0)
> -			return blknr;
> +		ret = read_allocated_block(node, i);
> +		if (ret < 0)
> +			return ret;
>  
> -		blknr = blknr << log2blocksize;
> +		blknr = ret << log2blocksize;
>  
>  		/* Last block.  */
>  		if (i == blockcnt - 1) {
> -- 
> 2.29.2
> 
> 
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