On Fri, Dec 02, 2022 at 09:30:56AM -0500, Waiman Long wrote:
On 12/2/22 05:18, Will Deacon wrote:
On Thu, Dec 01, 2022 at 12:03:39PM -0500, Waiman Long wrote:
On 12/1/22 08:44, Will Deacon wrote:
On Sun, Nov 27, 2022 at 08:44:41PM -0500, Waiman Long wrote:
Since commit 07ec77a1d4e8 ("sched: Allow task CPU affinity to be restricted on asymmetric systems"), the setting and clearing of user_cpus_ptr are done under pi_lock for arm64 architecture. However, dup_user_cpus_ptr() accesses user_cpus_ptr without any lock protection. When racing with the clearing of user_cpus_ptr in __set_cpus_allowed_ptr_locked(), it can lead to user-after-free and double-free in arm64 kernel.
Commit 8f9ea86fdf99 ("sched: Always preserve the user requested cpumask") fixes this problem as user_cpus_ptr, once set, will never be cleared in a task's lifetime. However, this bug was re-introduced in commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") which allows the clearing of user_cpus_ptr in do_set_cpus_allowed(). This time, it will affect all arches.
Fix this bug by always clearing the user_cpus_ptr of the newly cloned/forked task before the copying process starts and check the user_cpus_ptr state of the source task under pi_lock.
Note to stable, this patch won't be applicable to stable releases. Just copy the new dup_user_cpus_ptr() function over.
Fixes: 07ec77a1d4e8 ("sched: Allow task CPU affinity to be restricted on asymmetric systems") Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") CC: stable@vger.kernel.org Reported-by: David Wang 王标 wangbiao3@xiaomi.com Signed-off-by: Waiman Long longman@redhat.com
kernel/sched/core.c | 32 ++++++++++++++++++++++++++++---- 1 file changed, 28 insertions(+), 4 deletions(-)
As per my comments on the previous version of this patch:
https://lore.kernel.org/lkml/20221201133602.GB28489@willie-the-truck/T/#t
I think there are other issues to fix when racing affinity changes with fork() too.
It is certainly possible that there are other bugs hiding somewhere:-)
Right, but I actually took the time to hit the same race for the other affinity mask field so it seems a bit narrow-minded for us just to fix the one issue.
I focused on this particular one because of a double-free bug report from David. What other fields have you found to be subjected to data race?
See my other report linked above where we race on 'task_struct::cpus_mask'.
Will