From: Paul Jackson <[email protected]>
First of three -- this one goes before the container patches,
and should be sent to Linus for 2.6.22.
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" <[email protected]>
Cc: "Serge E. Hallyn" <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Herbert Poetzl <[email protected]>
Cc: Kirill Korotaev <[email protected]>
Cc: Paul Menage <[email protected]>
Cc: Srivatsa Vaddagiri <[email protected]>
Cc: Christoph Lameter <[email protected]>
Signed-off-by: Paul Jackson <[email protected]>
---
Andrew - this fix collides with the container changes, and now
that you have sent Christoph's patch to Linus to warn on writes
to zero-sized allocations, this fix should go to Linus too.
So it comes in three parts: fix the old, undo that, fix the new.
This patch should be applied first, before the container patches,
and sent to Linus for 2.6.22.
kernel/cpuset.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- 2.6.22-rc4-mm2.orig/kernel/cpuset.c 2007-06-08 14:44:58.899036450 -0700
+++ 2.6.22-rc4-mm2/kernel/cpuset.c 2007-06-08 14:47:00.996907442 -0700
@@ -1620,9 +1620,9 @@ static int pid_array_load(pid_t *pidarra
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);
--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <[email protected]> 1.650.933.1373
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