On 1/14/23 04:53, gregkh@linuxfoundation.org wrote:
The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
Possible dependencies:
87ca4f9efbd7 ("sched/core: Fix use-after-free bug in dup_user_cpus_ptr()") 8f9ea86fdf99 ("sched: Always preserve the user requested cpumask") 713a2e21a513 ("sched: Introduce affinity_context")
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 87ca4f9efbd7cc649ff43b87970888f2812945b8 Mon Sep 17 00:00:00 2001 From: Waiman Long longman@redhat.com Date: Fri, 30 Dec 2022 23:11:19 -0500 Subject: [PATCH] sched/core: Fix use-after-free bug in dup_user_cpus_ptr() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit
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. Since sched_setaffinity() can be invoked from another process, the process being modified may be undergoing fork() at the same time. When racing with the clearing of user_cpus_ptr in __set_cpus_allowed_ptr_locked(), it can lead to user-after-free and possibly 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.
I have a note here about what to do when backporting to stable. Just copy the new function over will be fine.
Cheers, Longman
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()") Reported-by: David Wang 王标 wangbiao3@xiaomi.com Signed-off-by: Waiman Long longman@redhat.com Signed-off-by: Ingo Molnar mingo@kernel.org Reviewed-by: Peter Zijlstra peterz@infradead.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20221231041120.440785-2-longman@redhat.com