Re: [PATCH RESEND] fs/befs: fix shift-out-of-bounds in befs_check_sb

[Manas Ghandat <ghandatmanas@gmail.com>]

Just a friendly ping :)

On 01/08/23 21:28, Manas Ghandat wrote:
> The consistency check for the block_size by using the block_shift caused
> integer overflow. Thus a max limit to the block_shift was defined named
> BEFS_MAX_BLOCK_SHIFT in befs.h. Also check for the block_shift was added
> so that overflow does not occur.
>
> Reported-by: syzbot+fc26c366038b54261e53@syzkaller.appspotmail.com
>
> Signed-off-by: Manas Ghandat <ghandatmanas@gmail.com>
> ---
>   fs/befs/befs.h  |  2 +-
>   fs/befs/super.c | 11 +++++++++++
>   2 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/fs/befs/befs.h b/fs/befs/befs.h
> index 7cd47245694d..5490024adb33 100644
> --- a/fs/befs/befs.h
> +++ b/fs/befs/befs.h
> @@ -13,7 +13,7 @@
>   
>   /* used in debug.c */
>   #define BEFS_VERSION "0.9.3"
> -
> +#define BEFS_MAX_BLOCK_SHIFT 31
>   
>   typedef u64 befs_blocknr_t;
>   /*
> diff --git a/fs/befs/super.c b/fs/befs/super.c
> index 7c50025c99d8..f2aeb2ed6e77 100644
> --- a/fs/befs/super.c
> +++ b/fs/befs/super.c
> @@ -88,6 +88,17 @@ befs_check_sb(struct super_block *sb)
>   		return BEFS_ERR;
>   	}
>   
> +	/*
> +	 * block_shift check added so that overflow does not
> +	 * occur during the block_size check
> +	 */
> +
> +	if (befs_sb->block_shift > BEFS_MAX_BLOCK_SHIFT) {
> +		befs_error(sb, "block_size too large. "
> +			   "Corruption likely.");
> +		return BEFS_ERR;
> +	}
> +
>   	/*
>   	 * block_shift and block_size encode the same information
>   	 * in different ways as a consistency check.