Re: [PATCH] Fix generic_block_fiemap for files bigger than 4GB

From: Andrew Morton
Date: Thu Oct 29 2009 - 02:01:03 EST


On Mon, 26 Oct 2009 18:24:28 +0100 Mike Hommey <mh@xxxxxxxxxxxx> wrote:

> Because of an integer overflow on start_blk, various kind of wrong results
> would be returned by the generic_block_fiemap handler, such as no extents
> when there is a 4GB+ hole at the beginning of the file, or wrong fe_logical
> when an extent starts after the first 4GB.
>
> Signed-off-by: Mike Hommey <mh@xxxxxxxxxxxx>
> ---
> fs/ioctl.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 7b17a14..6c75110 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -254,7 +254,7 @@ int __generic_block_fiemap(struct inode *inode,
> u64 len, get_block_t *get_block)
> {
> struct buffer_head tmp;
> - unsigned int start_blk;
> + unsigned long long start_blk;
> long long length = 0, map_len = 0;
> u64 logical = 0, phys = 0, size = 0;
> u32 flags = FIEMAP_EXTENT_MERGED;

Well. Should it be unsigned long long, or u64 or sector_t? Or even loff_t.

The code's a bit confused about types in there. And it's made much
more confusing by the moronic and wholly unnecessary use of macros for
blk_to_logical() and logical_to_blk().

It's also unhelpful that the `u64 start' argument forgot to get itself
documented in the kerneldoc comment. Sigh.

Ah, generic_block_fiemap() has it:

* @start: The initial block to map

I guess u64 was logical there as it comes in from userspace. But at
some boundary we should start talking kernel types so I suspect the
correct thing to do here is to use sector_t?

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