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Subject[PATCH 2/2] block: fix ioprio_get/set(IOPRIO_WHO_PGRP) vs setuid(2)
Date
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/set to take
the tasklist_lock in this case.

Fixes: d69b78ba1de (ioprio: grab rcu_read_lock in sys_ioprio_{set,get}())
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
block/ioprio.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/block/ioprio.c b/block/ioprio.c
index 77bcab11dce5..4ede2da961bb 100644
--- a/block/ioprio.c
+++ b/block/ioprio.c
@@ -119,11 +119,13 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
pgrp = task_pgrp(current);
else
pgrp = find_vpid(who);
+ read_lock(&tasklist_lock);
do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
ret = set_task_ioprio(p, ioprio);
if (ret)
break;
} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
+ read_unlock(&tasklist_lock);
break;
case IOPRIO_WHO_USER:
uid = make_kuid(current_user_ns(), who);
@@ -207,6 +209,7 @@ 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)
@@ -216,6 +219,7 @@ 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
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