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

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

[Dan Carpenter]

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@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;
 
-- 
2.39.2

Re: [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@linaro.org>

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

Re: [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@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@redhat.com>

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

[Dan Carpenter]

On Wed, Jul 26, 2023 at 01:56:29PM +0800, Baoquan He wrote:
> 
> Thanks for this fix. Just curious, this is found out by code exploring,
> or any breaking?

It's from static analysis, looking at when error codes are type promoted
to unsigned.  I pushed the Smatch check for this yesterday.

https://github.com/error27/smatch/commit/a2e6ca07e2ef83a72c9ffa3508af1398a6ecc7ed

regards,
dan carpenter

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

[Baoquan He]

On 07/26/23 at 09:03am, Dan Carpenter wrote:
> On Wed, Jul 26, 2023 at 01:56:29PM +0800, Baoquan He wrote:
> > 
> > Thanks for this fix. Just curious, this is found out by code exploring,
> > or any breaking?
> 
> It's from static analysis, looking at when error codes are type promoted
> to unsigned.  I pushed the Smatch check for this yesterday.

I see, thanks for telling.

> 
> https://github.com/error27/smatch/commit/a2e6ca07e2ef83a72c9ffa3508af1398a6ecc7ed
> 
> regards,
> dan carpenter
>