NACK/Cmnt: [PATCH] f2fs: fix a dead loop in f2fs_fiemap() Content-Type:

[Stefan Bader]

On 19.07.2018 18:35, Colin King wrote:
> From: Colin Ian King <colin.king at canonical.com>
> 
> CVE-2017-18257
> 
> A dead loop can be triggered in f2fs_fiemap() using the test case
> as below:
> 
>         ...
>         fd = open();
>         fallocate(fd, 0, 0, 4294967296);
>         ioctl(fd, FS_IOC_FIEMAP, fiemap_buf);
>         ...
> 
> It's caused by an overflow in __get_data_block():
>         ...
>         bh->b_size = map.m_len << inode->i_blkbits;
>         ...
> map.m_len is an unsigned int, and bh->b_size is a size_t which is 64 bits
> on 64 bits archtecture, type conversion from an unsigned int to a size_t
> will result in an overflow.
> 
> In the above-mentioned case, bh->b_size will be zero, and f2fs_fiemap()
> will call get_data_block() at block 0 again an again.
> 
> Fix this by adding a force conversion before left shift.
> 
> Signed-off-by: Wei Fang <fangwei1 at huawei.com>
> Acked-by: Chao Yu <yuchao0 at huawei.com>
> Signed-off-by: Jaegeuk Kim <jaegeuk at kernel.org>
> (backported from upstream commit b86e33075ed1909d8002745b56ecf73b833db143)
> Signed-off-by: Colin Ian King <colin.king at canonical.com>
> ---

I think that Trusty actually is just not affected and the tracker needs to have
hinting adjusted. fiemap looks to be only supported since v3.16:

Author: Jaegeuk Kim <jaegeuk at kernel.org>
Date:   Sun Jun 8 04:30:14 2014 +0900

    f2fs: support f2fs_fiemap

The replaced line actually has both blkbits and i as ints, so no conversion
happens there.

-Stefan

>  fs/f2fs/data.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index aa3438c..884bccc 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -455,7 +455,7 @@ static int get_data_block_ro(struct inode *inode, sector_t iblock,
>  				!= (dn.data_blkaddr + i)) || maxblocks == i)
>  				break;
>  		map_bh(bh_result, inode->i_sb, dn.data_blkaddr);
> -		bh_result->b_size = (i << blkbits);
> +		bh_result->b_size = ((u64)i << blkbits);
>  	}
>  	f2fs_put_dnode(&dn);
>  	trace_f2fs_get_data_block(inode, iblock, bh_result, 0);
> 


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