| From 950eaaca681c44aab87a46225c9e44f902c080aa Mon Sep 17 00:00:00 2001 |
| From: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
| Date: Tue, 31 Aug 2010 17:00:18 -0700 |
| Subject: pid: make setpgid() system call use RCU read-side critical section |
| |
| From: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
| |
| commit 950eaaca681c44aab87a46225c9e44f902c080aa upstream. |
| |
| [ 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. |
| |
| Reported-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
| Acked-by: David Howells <dhowells@redhat.com> |
| Cc: Jiri Slaby <jslaby@suse.cz> |
| Cc: Oleg Nesterov <oleg@redhat.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
| |
| --- |
| kernel/sys.c | 2 ++ |
| 1 file changed, 2 insertions(+) |
| |
| --- a/kernel/sys.c |
| +++ b/kernel/sys.c |
| @@ -962,6 +962,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid |
| pgid = pid; |
| if (pgid < 0) |
| return -EINVAL; |
| + rcu_read_lock(); |
| |
| /* From this point forward we keep holding onto the tasklist lock |
| * so that our parent does not change from under us. -DaveM |
| @@ -1015,6 +1016,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid |
| out: |
| /* All paths lead to here, thus we are safe. -DaveM */ |
| write_unlock_irq(&tasklist_lock); |
| + rcu_read_unlock(); |
| return err; |
| } |
| |