Re: [PATCH] connector: Fix sid connector (was: Badness at kernel/softirq.c:143...)

From: Evgeniy Polyakov
Date: Tue Sep 29 2009 - 10:07:27 EST


On Tue, Sep 29, 2009 at 03:47:21PM +0200, Christian Borntraeger (borntraeger@xxxxxxxxxx) wrote:
> Ok, can confirm that this patch fixes my problem, but I am not sure if the
> intended behaviour is still working as expected.

Your patch breaks assumption that task_session(current->group_leader) is
not equal to new session id, but to check task_session() we need either
rcu or task lock. Also setsid() return value is not zero or negative
error, but new session ID or negative error, so I believe attached patch
is a proper fix, although it looks rather ugly.

Also proc_sid_connector() uses GFP_KERNEL allocation which is way too
wrong to use under any locks.

Something like this (not tested :)

diff --git a/kernel/exit.c b/kernel/exit.c
index 5859f59..1565baf 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -359,10 +359,8 @@ void __set_special_pids(struct pid *pid)
{
struct task_struct *curr = current->group_leader;

- if (task_session(curr) != pid) {
+ if (task_session(curr) != pid)
change_pid(curr, PIDTYPE_SID, pid);
- proc_sid_connector(curr);
- }

if (task_pgrp(curr) != pid)
change_pid(curr, PIDTYPE_PGID, pid);
diff --git a/kernel/sys.c b/kernel/sys.c
index 255475d..b852a8b 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1090,6 +1090,7 @@ SYSCALL_DEFINE0(setsid)
struct pid *sid = task_pid(group_leader);
pid_t session = pid_vnr(sid);
int err = -EPERM;
+ int send_cn = 0;

write_lock_irq(&tasklist_lock);
/* Fail if I am already a session leader */
@@ -1104,12 +1105,18 @@ SYSCALL_DEFINE0(setsid)

group_leader->signal->leader = 1;
__set_special_pids(sid);
+ if (task_session(group_leader) != sid)
+ send_cn = 1;

proc_clear_tty(group_leader);

err = session;
out:
write_unlock_irq(&tasklist_lock);
+
+ if (send_cn)
+ proc_sid_connector(group_leader);
+
return err;
}


--
Evgeniy Polyakov
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/