linux-kernel - [PATCH v4 06/12] rlimits: allow setrlimit to non-current tasks

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Message-Id: <1277329933-8139-6-git-send-email-jslaby@suse.cz>
Date:	Wed, 23 Jun 2010 23:52:07 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	jirislaby@...il.com
Cc:	Oleg Nesterov <oleg@...hat.com>, akpm@...ux-foundation.org,
	adobriyan@...il.com, nhorman@...driver.com,
	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <jmorris@...ei.org>,
	Eric Paris <eparis@...isplace.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v4 06/12] rlimits: allow setrlimit to non-current tasks

From: Jiri Slaby <jirislaby@...il.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 sighand non-null. Do all the signal processing under
that lock still held.

There are some points:
1) security_task_setrlimit is now called with that lock held. This is
   not new, many security_* functions are called with this lock held
   already so it doesn't harm (all this security_* stuff does almost
   the same).
2) task->sighand->siglock (in update_rlimit_cpu) is nested in
   tasklist_lock. This dependence is already existing.
3) tsk->alloc_lock is nested in tasklist_lock. This is OK too, already
   existing dependence.

Signed-off-by: Jiri Slaby <jirislaby@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>
---
 kernel/sys.c |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index b5b96e3..9dbcbbc 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1272,6 +1272,7 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,
 
 #endif
 
+/* make sure you are allowed to change @tsk limits before calling this */
 int do_setrlimit(struct task_struct *tsk, unsigned int resource,
 		struct rlimit *new_rlim)
 {
@@ -1285,9 +1286,16 @@ int do_setrlimit(struct task_struct *tsk, unsigned int resource,
 	if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open)
 		return -EPERM;
 
+	/* protect tsk->signal and tsk->sighand from disappearing */
+	read_lock(&tasklist_lock);
+	if (!tsk->sighand) {
+		retval = -ESRCH;
+		goto out;
+	}
+
 	retval = security_task_setrlimit(tsk->group_leader, resource, new_rlim);
 	if (retval)
-		return retval;
+		goto out;
 
 	if (resource == RLIMIT_CPU && new_rlim->rlim_cur == 0) {
 		/*
@@ -1322,6 +1330,7 @@ int do_setrlimit(struct task_struct *tsk, unsigned int resource,
 
 	update_rlimit_cpu(tsk, new_rlim->rlim_cur);
 out:
+	read_unlock(&tasklist_lock);
 	return retval;
 }
 
-- 
1.7.1


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