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| author | Daniel J Blueman <daniel.blueman@gmail.com> | 2010-11-09 21:33:02 +0100 |
|---|---|---|
| committer | Jens Axboe <jaxboe@fusionio.com> | 2010-11-10 14:40:53 +0100 |
| commit | 1447399b3e34af016c368b4178db7ef0e04e15b0 (patch) | |
| tree | e5de50c5520b2c20359c2afbf903e052b88bb995 /fs/ioprio.c | |
| parent | a014741c0adfb8fb79952939ca087cf03d272bb9 (diff) | |
| download | linux-1447399b3e34af016c368b4178db7ef0e04e15b0.tar.gz linux-1447399b3e34af016c368b4178db7ef0e04e15b0.tar.bz2 linux-1447399b3e34af016c368b4178db7ef0e04e15b0.zip | |
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.c | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/fs/ioprio.c b/fs/ioprio.c index 748cfb92dcc6..8def14e24c37 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) |