linux-kernel - Re: [PATCH] bfs: Fix sanity checks for empty files

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Date:   Tue, 9 May 2017 21:29:10 +0100
From:   Tigran Aivazian <tigran@...azian.fsnet.co.uk>
To:     Rakesh Pandit <rakesh@...era.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bfs: Fix sanity checks for empty files

Hi,

If you had created the filesystem with the proper mkfs under SCO
UnixWare 7 you (probably) wouldn't encounter this issue. But since
commercial Unix-es are now part of history and the only proper way is
the Linux mkfs.bfs utility, your patch is fine.

Kind regards,
Tigran

On 5 May 2017 at 21:16, Rakesh Pandit <rakesh@...era.com> wrote:
> Mount fails if file system image has empty files because of sanity
> check while reading superblock. For empty files disk offset to end of
> file (i_eoffset) is cpu_to_le32(-1). Sanity check comparison, which
> compares disk offset with file system size isn't valid for this value
> and hence is ignored with this patch.
>
> Steps to reproduce:
>
> $  dd if=/dev/zero of=bfs-image count=204800
> $  mkfs.bfs bfs-image
> $  mkdir bfs-mount-point
> $  sudo mount -t bfs -o loop bfs-image bfs-mount-point/
> $  cd bfs-mount-point/
> $  sudo touch a
> $  cd ..
> $  sudo umount bfs-mount-point/
> $  sudo mount -t bfs -o loop bfs-image bfs-mount-point/
> mount: /dev/loop0: can't read superblock
>
> $  dmesg
> [25526.689580] BFS-fs: bfs_fill_super(): Inode 0x00000003 corrupted
>
> Signed-off-by: Rakesh Pandit <rakesh@...era.com>
> ---
>
> This was sent three years but maintainer has been unresponsive:
> https://marc.info/?l=linux-kernel&m=138980764525250
>
> So sending you Andrew as previous patches to bfs have gone through
> your tree.  This is tested and reproducible.
>
>  fs/bfs/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/bfs/inode.c b/fs/bfs/inode.c
> index f2deec0..0d3dc18 100644
> --- a/fs/bfs/inode.c
> +++ b/fs/bfs/inode.c
> @@ -419,7 +419,7 @@ static int bfs_fill_super(struct super_block *s, void *data, int silent)
>                 if (i_sblock > info->si_blocks ||
>                         i_eblock > info->si_blocks ||
>                         i_sblock > i_eblock ||
> -                       i_eoff > s_size ||
> +                       (i_eoff != le32_to_cpu(-1) && i_eoff > s_size) ||
>                         i_sblock * BFS_BSIZE > i_eoff) {
>
>                         printf("Inode 0x%08x corrupted\n", i);
> --
> 2.9.3
>