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

[Matthew Wilcox]

On Tue, Jul 25, 2023 at 08:03:16PM +0300, 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>

Reviewed-by: Matthew Wilcox (Oracle) <willy at infradead.org>