Messages in this thread Patch in this message | | | Date | Mon, 30 Aug 2010 10:26:31 -0700 | From | "Paul E. McKenney" <> | Subject | [PATCH RFC] pid: make setpgid() system call use RCU read-side critical section |
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[ 23.584719] [ 23.584720] =================================================== [ 23.585059] [ INFO: suspicious rcu_dereference_check() usage. ] [ 23.585176] --------------------------------------------------- [ 23.585176] kernel/pid.c:419 invoked rcu_dereference_check() without protection! [ 23.585176] [ 23.585176] other info that might help us debug this: [ 23.585176] [ 23.585176] [ 23.585176] rcu_scheduler_active = 1, debug_locks = 1 [ 23.585176] 1 lock held by rc.sysinit/728: [ 23.585176] #0: (tasklist_lock){.+.+..}, at: [<ffffffff8104771f>] sys_setpgid+0x5f/0x193 [ 23.585176] [ 23.585176] stack backtrace: [ 23.585176] Pid: 728, comm: rc.sysinit Not tainted 2.6.36-rc2 #2 [ 23.585176] Call Trace: [ 23.585176] [<ffffffff8105b436>] lockdep_rcu_dereference+0x99/0xa2 [ 23.585176] [<ffffffff8104c324>] find_task_by_pid_ns+0x50/0x6a [ 23.585176] [<ffffffff8104c35b>] find_task_by_vpid+0x1d/0x1f [ 23.585176] [<ffffffff81047727>] sys_setpgid+0x67/0x193 [ 23.585176] [<ffffffff810029eb>] system_call_fastpath+0x16/0x1b [ 24.959669] type=1400 audit(1282938522.956:4): avc: denied { module_request } for pid=766 comm="hwclock" kmod="char-major-10-135" scontext=system_u:system_r:hwclock_t:s0 tcontext=system_u:system_r:kernel_t:s0 tclas
It turns out that the setpgid() system call fails to enter an RCU read-side critical section before doing a PID-to-task_struct translation. This commit therefore does rcu_read_lock() before the translation, and also does rcu_read_unlock() after the last use of the returned pointer.
Located-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> ---
sys.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/kernel/sys.c b/kernel/sys.c index e9ad444..05a4b0c 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -938,6 +938,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid_t, pgid) write_lock_irq(&tasklist_lock); err = -ESRCH; + rcu_read_lock(); p = find_task_by_vpid(pid); if (!p) goto out; @@ -983,6 +984,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid_t, pgid) err = 0; out: /* All paths lead to here, thus we are safe. -DaveM */ + rcu_read_unlock(); write_unlock_irq(&tasklist_lock); return err; }
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