]> pilppa.com Git - linux-2.6-omap-h63xx.git/commit
cpuset: zero malloc - revert the old cpuset fix
authorPaul Jackson <pj@sgi.com>
Fri, 19 Oct 2007 06:39:28 +0000 (23:39 -0700)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Fri, 19 Oct 2007 18:53:35 +0000 (11:53 -0700)
commit55a230aae650157720becc09cadb7d10efbf5013
treea4d85dd865c4e939580fdde986a0d29912e45a7e
parent8f731f7d83d6c6a3eeb32cce79bfcddbf7fac8cc
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