linux-kernel - Re: [PATCH][RESEND] mac: validate mac

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Message-ID: <x49610wcq84.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 20 Nov 2015 16:31:39 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RESEND] mac: validate mac_partition is within sector

Kees Cook <keescook@...omium.org> writes:

> If md->signature == MAC_DRIVER_MAGIC and md->block_size == 1023, a single
> 512 byte sector would be read (secsize / 512). However the partition
> structure would be located past the end of the buffer (secsize % 512).

Do we even want to support non-power-of-two block sizes?

-Jeff

>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Cc: stable@...r.kernel.org
> ---
> There doesn't seem to be a mac partition maintainer...
> ---
>  block/partitions/mac.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/block/partitions/mac.c b/block/partitions/mac.c
> index c2c48ec64b27..621317ac4d59 100644
> --- a/block/partitions/mac.c
> +++ b/block/partitions/mac.c
> @@ -32,7 +32,7 @@ int mac_partition(struct parsed_partitions *state)
>  	Sector sect;
>  	unsigned char *data;
>  	int slot, blocks_in_map;
> -	unsigned secsize;
> +	unsigned secsize, datasize, partoffset;
>  #ifdef CONFIG_PPC_PMAC
>  	int found_root = 0;
>  	int found_root_goodness = 0;
> @@ -50,10 +50,14 @@ int mac_partition(struct parsed_partitions *state)
>  	}
>  	secsize = be16_to_cpu(md->block_size);
>  	put_dev_sector(sect);
> -	data = read_part_sector(state, secsize/512, &sect);
> +	datasize = round_down(secsize, 512);
> +	data = read_part_sector(state, datasize / 512, &sect);
>  	if (!data)
>  		return -1;
> -	part = (struct mac_partition *) (data + secsize%512);
> +	partoffset = secsize % 512;
> +	if (partoffset + sizeof(*part) > datasize)
> +		return -1;
> +	part = (struct mac_partition *) (data + partoffset);
>  	if (be16_to_cpu(part->signature) != MAC_PARTITION_MAGIC) {
>  		put_dev_sector(sect);
>  		return 0;		/* not a MacOS disk */
> -- 
> 1.9.1
--
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