From 55a230aae650157720becc09cadb7d10efbf5013 Mon Sep 17 00:00:00 2001
From: Paul Jackson <pj@sgi.com>
Date: Thu, 18 Oct 2007 23:39:28 -0700
Subject: [PATCH] cpuset: zero malloc - revert the old cpuset fix
The cpuset code to present a list of tasks using a cpuset to user space could
write to an array that it had kmalloc'd, after a kmalloc request of zero size.
The problem was that the code didn't check for writes past the allocated end
of the array until -after- the first write.
This is a race condition that is likely rare -- it would only show up if a
cpuset went from being empty to having a task in it, during the brief time
between the allocation and the first write.
Prior to roughly 2.6.22 kernels, this was also a benign problem, because a
zero kmalloc returned a few usable bytes anyway, and no harm was done with the
bogus write.
With the 2.6.22 kernel changes to make issue a warning if code tries to write
to the location returned from a zero size allocation, this problem is no
longer benign. This cpuset code would occassionally trigger that warning.
The fix is trivial -- check before storing into the array, not after, whether
the array is big enough to hold the store.
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Serge E. Hallyn" <serue@us.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Kirill Korotaev <dev@openvz.org>
Cc: Paul Menage <menage@google.com>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
kernel/cpuset.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 64950fa5d321..a40a2c4384b3 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1638,9 +1638,9 @@ static int pid_array_load(pid_t *pidarray, int npids, struct cpuset *cs)
do_each_thread(g, p) {
if (p->cpuset == cs) {
+ pidarray[n++] = p->pid;
if (unlikely(n == npids))
goto array_full;
- pidarray[n++] = p->pid;
}
} while_each_thread(g, p);
--
2.20.1