linux-ext4 - Re: [PATCH 1/3] ext4: sanity check the block and cluster size at mount time

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Message-Id: <DF4FD9C9-580B-4DBE-BD88-6E7067EC69E9@dilger.ca>
Date:   Fri, 18 Nov 2016 01:38:10 -0700
From:   Andreas Dilger <adilger@...ger.ca>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>, kernel@...p.com,
        bp@...en8.de, stable@...r.kernel.org
Subject: Re: [PATCH 1/3] ext4: sanity check the block and cluster size at mount time

On Nov 17, 2016, at 9:26 PM, Theodore Ts'o <tytso@....edu> wrote:
> 
> If the block size or cluster size is insane, reject the mount.  This
> is important for security reasons (although we shouldn't be just
> depending on this check).
> 
> Ref: http://www.securityfocus.com/archive/1/539661
> Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1332506
> Reported-by: Borislav Petkov <bp@...en8.de>
> Reported-by: Nikolay Borisov <kernel@...p.com>
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> Cc: stable@...r.kernel.org
> ---
> fs/ext4/ext4.h  |  1 +
> fs/ext4/super.c | 17 ++++++++++++++++-
> 2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 35ccbdc2d64e..12f50ef56fe1 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3567,7 +3567,15 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> 	if (blocksize < EXT4_MIN_BLOCK_SIZE ||
> 	    blocksize > EXT4_MAX_BLOCK_SIZE) {
> 		ext4_msg(sb, KERN_ERR,
> -		       "Unsupported filesystem blocksize %d", blocksize);
> +		       "Unsupported filesystem blocksize %d (%d)",

Would be good to indicate what the second value is, like "(%d bits)".

Cheers, Andreas

> +			 blocksize, le32_to_cpu(es->s_log_block_size));
> +		goto failed_mount;
> +	}
> +	if (le32_to_cpu(es->s_log_block_size) >
> +	    (EXT4_MAX_BLOCK_LOG_SIZE - EXT4_MIN_BLOCK_LOG_SIZE)) {
> +		ext4_msg(sb, KERN_ERR,
> +			 "Invalid log block size: %u",
> +			 le32_to_cpu(es->s_log_block_size));
> 		goto failed_mount;
> 	}
> 
> @@ -3699,6 +3707,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> 				 "block size (%d)", clustersize, blocksize);
> 			goto failed_mount;
> 		}
> +		if (le32_to_cpu(es->s_log_cluster_size) >
> +		    (EXT4_MAX_CLUSTER_LOG_SIZE - EXT4_MIN_BLOCK_LOG_SIZE)) {
> +			ext4_msg(sb, KERN_ERR,
> +				 "Invalid log cluster size: %u",
> +				 le32_to_cpu(es->s_log_cluster_size));
> +			goto failed_mount;
> +		}
> 		sbi->s_cluster_bits = le32_to_cpu(es->s_log_cluster_size) -
> 			le32_to_cpu(es->s_log_block_size);
> 		sbi->s_clusters_per_group =
> --
> 2.11.0.rc0.7.gbe5a750
> 
> --
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Cheers, Andreas






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