Re: [PATCH v2 02/22] coredump: refuse negative skips

[R Nageswara Sastry <rnsastry@linux.ibm.com>]

On 20.08.2026 4:39 AM, Christian Brauner wrote:
> The dump_skip_to() helper calculates a relative skip based on the
> absolute positon of the coredump:
>
> 	cprm->to_skip = pos - cprm->pos;
>
> That's easy to mess up for callers and one already did. This risk
> endless zero PAGE_SIZE loops or overwriting already written coredump
> data thereby corrupting the dump.
>
> I don't think skipping backwards has any meaning. So warn and refuse.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Tested-by: R Nageswara Sastry <rnsastry@linux.ibm.com>

System: ppc64le LPAR (IBM POWER), Linux 7.3-rc2
> ---
>   fs/coredump.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index e68a76ff92a3..ac4e922c9cb9 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -1261,6 +1261,8 @@ EXPORT_SYMBOL(dump_emit);
>   
>   void dump_skip_to(struct coredump_params *cprm, unsigned long pos)
>   {
> +	if (WARN_ON_ONCE(pos < cprm->pos))
> +		return;
>   	cprm->to_skip = pos - cprm->pos;
>   }
>   EXPORT_SYMBOL(dump_skip_to);
>
-- 
Thanks and Regards
R.Nageswara Sastry