[PATCH 5/6] core: allow setrlimit to non-current tasks

[Jiri Slaby <jirislaby@gmail.com>]

Add locking to allow setrlimit accept task parameter other than
current.

Namely, lock tasklist_lock for read and check whether the task
structure has signal and sighand non-null. Do all the signal
processing under that lock still held.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
---
 kernel/sys.c |   26 ++++++++++++++++++++------
 1 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 919cebe..777a152 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1244,16 +1244,27 @@ int setrlimit(struct task_struct *tsk, unsigned int resource,
 
 	if (new_rlim->rlim_cur > new_rlim->rlim_max)
 		return -EINVAL;
+
+	/* protect tsk->signal and tsk->sighand from disappearing */
+	read_lock_irq(&tasklist_lock);
+	if (!tsk->signal || !tsk->sighand) {
+		retval = -ESRCH;
+		goto unlock;
+	}
 	old_rlim = tsk->signal->rlim + resource;
 	if ((new_rlim->rlim_max > old_rlim->rlim_max) &&
-	    !capable(CAP_SYS_RESOURCE))
-		return -EPERM;
-	if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open)
-		return -EPERM;
+	    !capable(CAP_SYS_RESOURCE)) {
+		retval = -EPERM;
+		goto unlock;
+	}
+	if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open) {
+		retval = -EPERM;
+		goto unlock;
+	}
 
 	retval = security_task_setrlimit(tsk, resource, new_rlim);
 	if (retval)
-		return retval;
+		goto unlock;
 
 	if (resource == RLIMIT_CPU && new_rlim->rlim_cur == 0) {
 		/*
@@ -1283,7 +1294,10 @@ int setrlimit(struct task_struct *tsk, unsigned int resource,
 
 	update_rlimit_cpu(tsk, new_rlim->rlim_cur);
 out:
-	return 0;
+	retval = 0;
+unlock:
+	read_unlock_irq(&tasklist_lock);
+	return retval;
 }
 
 SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim)
-- 
1.6.3.3