This is a note to let you know that I've just added the patch titled block: fix ioprio_get(IOPRIO_WHO_PGRP) vs setuid(2) to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: block-fix-ioprio_get-ioprio_who_pgrp-vs-setuid-2.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From e6a59aac8a8713f335a37d762db0dbe80e7f6d38 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso <dave@xxxxxxxxxxxx> Date: Fri, 10 Dec 2021 10:20:58 -0800 Subject: block: fix ioprio_get(IOPRIO_WHO_PGRP) vs setuid(2) From: Davidlohr Bueso <dave@xxxxxxxxxxxx> commit e6a59aac8a8713f335a37d762db0dbe80e7f6d38 upstream. 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 <oleg@xxxxxxxxxx> Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx> Link: https://lore.kernel.org/r/20211210182058.43417-1-dave@xxxxxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- block/ioprio.c | 3 +++ 1 file changed, 3 insertions(+) --- a/block/ioprio.c +++ b/block/ioprio.c @@ -202,6 +202,7 @@ SYSCALL_DEFINE2(ioprio_get, int, which, 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) @@ -211,6 +212,8 @@ SYSCALL_DEFINE2(ioprio_get, int, which, 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); Patches currently in stable-queue which might be from dave@xxxxxxxxxxxx are queue-4.4/block-fix-ioprio_get-ioprio_who_pgrp-vs-setuid-2.patch