2022-03-28 03:28:34

by Xiaomeng Tong

Subject: [PATCH] md: fix missing check on list iterator

The bug is here:
bypass_pg(m, pg, bypassed);

The list iterator 'pg' will point to a bogus position containing
HEAD if the list is empty or no element is found. This case must
be checked before any use of the iterator, otherwise it will lead
to a invalid memory access.

To fix this bug, run bypass_pg(m, pg, bypassed); and return 0
when found, otherwise return -EINVAL.

Cc: [email protected]
Fixes: ^1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Xiaomeng Tong <[email protected]>
---
drivers/md/dm-mpath.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index f4719b65e5e3..6ba8f1133564 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1496,12 +1496,13 @@ static int bypass_pg_num(struct multipath *m, const char *pgstr, bool bypassed)
}

list_for_each_entry(pg, &m->priority_groups, list) {
- if (!--pgnum)
- break;
+ if (!--pgnum) {
+ bypass_pg(m, pg, bypassed);
+ return 0;
+ }
}

- bypass_pg(m, pg, bypassed);
- return 0;
+ return -EINVAL;
}

/*
--
2.17.1

2022-04-05 00:52:21

by Mike Snitzer

Subject: Re: md: fix missing check on list iterator

On Sun, Mar 27 2022 at 1:37P -0400,
Xiaomeng Tong <[email protected]> wrote:

> The bug is here:
> bypass_pg(m, pg, bypassed);
>
> The list iterator 'pg' will point to a bogus position containing
> HEAD if the list is empty or no element is found. This case must
> be checked before any use of the iterator, otherwise it will lead
> to a invalid memory access.
>
> To fix this bug, run bypass_pg(m, pg, bypassed); and return 0
> when found, otherwise return -EINVAL.
>
> Cc: [email protected]
> Fixes: ^1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Xiaomeng Tong <[email protected]>
> ---
> drivers/md/dm-mpath.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index f4719b65e5e3..6ba8f1133564 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -1496,12 +1496,13 @@ static int bypass_pg_num(struct multipath *m, const char *pgstr, bool bypassed)
> }
>
> list_for_each_entry(pg, &m->priority_groups, list) {
> - if (!--pgnum)
> - break;
> + if (!--pgnum) {
> + bypass_pg(m, pg, bypassed);
> + return 0;
> + }
> }
>
> - bypass_pg(m, pg, bypassed);
> - return 0;
> + return -EINVAL;
> }
>
> /*
> --
> 2.17.1
>

Did you acually hit a bug (invalid memory access)?

I cannot see how given the checks prior to iterating m->priority_groups:

if (!pgstr || (sscanf(pgstr, "%u%c", &pgnum, &dummy) != 1) || !pgnum ||
!m->nr_priority_groups || (pgnum > m->nr_priority_groups)) {
DMWARN("invalid PG number supplied to bypass_pg");
return -EINVAL;
}

So I have _not_ taken your "fix".

2022-04-05 01:09:43

by Xiaomeng Tong

Subject: Re: md: fix missing check on list iterator

On Fri, 1 Apr 2022 10:47:18 -0400, Mike Snitzer wrote:
> Did you acually hit a bug (invalid memory access)?
>
> I cannot see how given the checks prior to iterating m->priority_groups:
>
> if (!pgstr || (sscanf(pgstr, "%u%c", &pgnum, &dummy) != 1) || !pgnum ||
> !m->nr_priority_groups || (pgnum > m->nr_priority_groups)) {
> DMWARN("invalid PG number supplied to bypass_pg");
> return -EINVAL;
> }
>
> So I have _not_ taken your "fix".

Yes, you are correct. It has been checked before, thus not a bug and
no need to fix. And I have sent a PATCH v2 to use list iterator only
inside the loop, please check it. Thank you very much.

--
Xiaomeng Tong