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authorDaniel J Blueman <daniel.blueman@gmail.com>2010-11-09 21:33:02 +0100
committerJens Axboe <jaxboe@fusionio.com>2010-11-10 14:40:53 +0100
commit1447399b3e34af016c368b4178db7ef0e04e15b0 (patch)
treee5de50c5520b2c20359c2afbf903e052b88bb995 /fs/ioprio.c
parenta014741c0adfb8fb79952939ca087cf03d272bb9 (diff)
downloadlinux-1447399b3e34af016c368b4178db7ef0e04e15b0.tar.gz
ioprio: fix RCU locking around task dereference
With 2.6.37-rc1, I observe sys_ioprio_set not taking the RCU lock [1] across access to the task credentials. Inspecting the code in fs/ioprio.c, the tasklist_lock is held for read across the __task_cred call, which is presumably sufficient to prevent the task credentials becoming stale. =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- kernel/pid.c:419 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 1 lock held by start-stop-daem/2246: #0: (tasklist_lock){.?.?..}, at: [<ffffffff811a2dfa>] sys_ioprio_set+0x8a/0x400 stack backtrace: Pid: 2246, comm: start-stop-daem Not tainted 2.6.37-rc1-330cd+ #2 Call Trace: [<ffffffff8109f5f4>] lockdep_rcu_dereference+0xa4/0xc0 [<ffffffff81085651>] find_task_by_pid_ns+0x81/0x90 [<ffffffff8108567d>] find_task_by_vpid+0x1d/0x20 [<ffffffff811a3160>] sys_ioprio_set+0x3f0/0x400 [<ffffffff816efa79>] ? trace_hardirqs_on_thunk+0x3a/0x3f [<ffffffff81003482>] system_call_fastpath+0x16/0x1b Take the RCU lock for read across acquiring the pointer to the task credentials and dereferencing it. Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com> Fixed up by Jens to fix missing rcu_read_unlock() on mismatches. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'fs/ioprio.c')
-rw-r--r--fs/ioprio.c14
1 files changed, 12 insertions, 2 deletions
diff --git a/fs/ioprio.c b/fs/ioprio.c
index 748cfb92dcc..8def14e24c3 100644
--- a/fs/ioprio.c
+++ b/fs/ioprio.c
@@ -139,7 +139,12 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
break;
do_each_thread(g, p) {
- if (__task_cred(p)->uid != who)
+ int match;
+
+ rcu_read_lock();
+ match = __task_cred(p)->uid == who;
+ rcu_read_unlock();
+ if (!match)
continue;
ret = set_task_ioprio(p, ioprio);
if (ret)
@@ -232,7 +237,12 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
break;
do_each_thread(g, p) {
- if (__task_cred(p)->uid != user->uid)
+ int match;
+
+ rcu_read_lock();
+ match = __task_cred(p)->uid == user->uid;
+ rcu_read_unlock();
+ if (!match)
continue;
tmpio = get_task_ioprio(p);
if (tmpio < 0)