[PATCH] proc/vmcore: fix signedness bug in read_from_oldmem()

[Baoquan He]

Hi Dan,

On 07/25/23 at 08:03pm, Dan Carpenter wrote:
> The bug is the error handling:
> 
> 	if (tmp < nr_bytes) {
> 
> "tmp" can hold negative error codes but because "nr_bytes" is type
> size_t the negative error codes are treated as very high positive
> values (success).  Fix this by changing "nr_bytes" to type ssize_t.  The
> "nr_bytes" variable is used to store values between 1 and PAGE_SIZE and
> they can fit in ssize_t without any issue.
> 
> Fixes: 5d8de293c224 ("vmcore: convert copy_oldmem_page() to take an iov_iter")
> Signed-off-by: Dan Carpenter <dan.carpenter at linaro.org>
> ---
>  fs/proc/vmcore.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index cb80a7703d58..1fb213f379a5 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -132,7 +132,7 @@ ssize_t read_from_oldmem(struct iov_iter *iter, size_t count,
>  			 u64 *ppos, bool encrypted)
>  {
>  	unsigned long pfn, offset;
> -	size_t nr_bytes;
> +	ssize_t nr_bytes;
>  	ssize_t read = 0, tmp;
>  	int idx;

Thanks for this fix. Just curious, this is found out by code exploring,
or any breaking?

Acked-by: Baoquan He <bhe at redhat.com>