On 1/14/23 04:53, gregkh@xxxxxxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxx>.
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@xxxxxxxxxx>
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
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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@xxxxxxxxxx>
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20221231041120.440785-2-longman@xxxxxxxxxx
