2021-12-10 18:21:09

by Davidlohr Bueso

Subject: [PATCH] block: fix ioprio_get(IOPRIO_WHO_PGRP) vs setuid(2)

do_each_pid_thread(PIDTYPE_PGID) can race with a concurrent
change_pid(PIDTYPE_PGID) that can move the task from one hlist
to another while iterating. Serialize ioprio_get to take
the tasklist_lock in this case, just like it's set counterpart.

Fixes: d69b78ba1de (ioprio: grab rcu_read_lock in sys_ioprio_{set,get}())
Acked-by: Oleg Nesterov <[email protected]>
Signed-off-by: Davidlohr Bueso <[email protected]>
---
This is basically a resend of https://lore.kernel.org/all/[email protected]/
with Oleg's ack and without the ioprio_set part as this was fixed
later after this patch was lost for whatever reason.

block/ioprio.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/block/ioprio.c b/block/ioprio.c
index 313c14a70bbd..6f01d35a5145 100644
--- a/block/ioprio.c
+++ b/block/ioprio.c
@@ -220,6 +220,7 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
pgrp = task_pgrp(current);
else
pgrp = find_vpid(who);
+ read_lock(&tasklist_lock);
do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
tmpio = get_task_ioprio(p);
if (tmpio < 0)
@@ -229,6 +230,8 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
else
ret = ioprio_best(ret, tmpio);
} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
+ read_unlock(&tasklist_lock);
+
break;
case IOPRIO_WHO_USER:
uid = make_kuid(current_user_ns(), who);
--
2.26.2

2021-12-10 18:26:18

by Jens Axboe

Subject: Re: [PATCH] block: fix ioprio_get(IOPRIO_WHO_PGRP) vs setuid(2)

On Fri, 10 Dec 2021 10:20:58 -0800, Davidlohr Bueso wrote:
> do_each_pid_thread(PIDTYPE_PGID) can race with a concurrent
> change_pid(PIDTYPE_PGID) that can move the task from one hlist
> to another while iterating. Serialize ioprio_get to take
> the tasklist_lock in this case, just like it's set counterpart.
>
>

Applied, thanks!

[1/1] block: fix ioprio_get(IOPRIO_WHO_PGRP) vs setuid(2)
commit: e6a59aac8a8713f335a37d762db0dbe80e7f6d38

Best regards,
--
Jens Axboe