[PATCH] um: ubd: Fix crash from option parsing

[PATCH] um: ubd: Fix crash from option parsing

[Paul Lawrence]

Below patch will cause NULL ptr dereferences if the optional filenames
are not present.

Fixes: ef3ba87cb7c9 (um: ubd: Set device serial attribute from cmdline)
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 arch/um/drivers/ubd_kern.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 13b1fe694b90..704989088f28 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -371,15 +371,15 @@ static int ubd_setup_common(char *str, int *index_out, char **error_out)
 
 break_loop:
 	file = strsep(&str, ",:");
-	if (*file == '\0')
+	if (file && *file == '\0')
 		file = NULL;
 
 	backing_file = strsep(&str, ",:");
-	if (*backing_file == '\0')
+	if (backing_file && *backing_file == '\0')
 		backing_file = NULL;
 
 	serial = strsep(&str, ",:");
-	if (*serial == '\0')
+	if (serial && *serial == '\0')
 		serial = NULL;
 
 	if (backing_file && ubd_dev->no_cow) {
-- 
2.30.0.284.gd98b1dd5eaa7-goog

Re: [PATCH] um: ubd: Fix crash from option parsing

[Gabriel Krisman Bertazi]

Paul Lawrence <paullawrence@google.com> writes:

> Below patch will cause NULL ptr dereferences if the optional filenames
> are not present.
>
> Fixes: ef3ba87cb7c9 (um: ubd: Set device serial attribute from cmdline)
> Signed-off-by: Paul Lawrence <paullawrence@google.com>

Looks good.

Reviewed-by: Gabriel Krisman Bertazi <krisman@collabora.com>

Totally unrelated, but it seems the original patch writes a "(null)"
string to the sysfs attribute, if no serial is defined.  I think we
should have a default serial UBDX in case the user didn't provide any.

Thanks,

> ---
>  arch/um/drivers/ubd_kern.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
> index 13b1fe694b90..704989088f28 100644
> --- a/arch/um/drivers/ubd_kern.c
> +++ b/arch/um/drivers/ubd_kern.c
> @@ -371,15 +371,15 @@ static int ubd_setup_common(char *str, int *index_out, char **error_out)
>  
>  break_loop:
>  	file = strsep(&str, ",:");
> -	if (*file == '\0')
> +	if (file && *file == '\0')
>  		file = NULL;
>  
>  	backing_file = strsep(&str, ",:");
> -	if (*backing_file == '\0')
> +	if (backing_file && *backing_file == '\0')
>  		backing_file = NULL;
>  
>  	serial = strsep(&str, ",:");
> -	if (*serial == '\0')
> +	if (serial && *serial == '\0')
>  		serial = NULL;
>  
>  	if (backing_file && ubd_dev->no_cow) {

-- 
Gabriel Krisman Bertazi

Re: [PATCH] um: ubd: Fix crash from option parsing

[Hajime Tazaki]

Hello,

On Wed, 20 Jan 2021 03:19:45 +0900,
Paul Lawrence wrote:
> 
> Below patch will cause NULL ptr dereferences if the optional filenames
> are not present.
> 
> Fixes: ef3ba87cb7c9 (um: ubd: Set device serial attribute from cmdline)
> Signed-off-by: Paul Lawrence <paullawrence@google.com>

This was addressed/fixed by the below patch, though that one doesn't
the first "file" variable check.

http://lists.infradead.org/pipermail/linux-um/2020-December/000983.html

There was another attempt to fix (with the same diff), btw.

http://lists.infradead.org/pipermail/linux-um/2021-January/000998.html

It seems that the patch is already queued but not upstreamed yet.

-- Hajime

Re: [PATCH] um: ubd: Fix crash from option parsing

[Paul Lawrence]

> This was addressed/fixed by the below patch, though that one doesn't
> the first "file" variable check.

I don't believe the first file variable can in fact be NULL, so my check was
unnecessary. Pleased to see this has been fixed, we can abandon my patch now.

Paul