2021-01-19 18:23:48

by Paul Lawrence

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

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 <[email protected]>
---
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

2021-01-19 18:43:19

by Gabriel Krisman Bertazi

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

Paul Lawrence <[email protected]> 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 <[email protected]>

Looks good.

Reviewed-by: Gabriel Krisman Bertazi <[email protected]>

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

2021-01-22 00:43:44

by Hajime Tazaki

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

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 <[email protected]>

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

2021-01-22 14:47:53

by Paul Lawrence

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

> 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