2023-01-15 19:44:35

by Waiman Long

Subject: [PATCH] sched/core: Fix NULL pointer access fault in sched_setaffinity() with non-SMP configs

The kernel commit 9a5418bc48ba ("sched/core: Use kfree_rcu() in
do_set_cpus_allowed()") introduces a bug for kernels built with non-SMP
configs. Calling sched_setaffinity() on such a uniprocessor kernel will
cause cpumask_copy() to be called with a NULL pointer leading to general
protection fault. This is not really a problem in real use cases as
there aren't that many uniprocessor kernel configs in use and calling
sched_setaffinity() on such a uniprocessor system doesn't make sense.

Fix this problem by making sure cpumask_copy() will not be called in
such a case.

Fixes: 9a5418bc48ba ("sched/core: Use kfree_rcu() in do_set_cpus_allowed()")
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
---
kernel/sched/core.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bb1ee6d7bdde..e838feb6adc5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8290,12 +8290,18 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
if (retval)
goto out_put_task;

+ /*
+ * With non-SMP configs, user_cpus_ptr/user_mask isn't used and
+ * alloc_user_cpus_ptr() returns NULL.
+ */
user_mask = alloc_user_cpus_ptr(NUMA_NO_NODE);
- if (IS_ENABLED(CONFIG_SMP) && !user_mask) {
+ if (user_mask) {
+ cpumask_copy(user_mask, in_mask);
+ } else if (IS_ENABLED(CONFIG_SMP)) {
retval = -ENOMEM;
goto out_put_task;
}
- cpumask_copy(user_mask, in_mask);
+
ac = (struct affinity_context){
.new_mask = in_mask,
.user_mask = user_mask,
--
2.31.1

2023-01-16 09:30:28

by tip-bot2 for Haifeng Xu

Subject: [tip: sched/urgent] sched/core: Fix NULL pointer access fault in sched_setaffinity() with non-SMP configs

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID: 5657c116783545fb49cd7004994c187128552b12
Gitweb: https://git.kernel.org/tip/5657c116783545fb49cd7004994c187128552b12
Author: Waiman Long <[email protected]>
AuthorDate: Sun, 15 Jan 2023 14:31:22 -05:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Mon, 16 Jan 2023 10:07:25 +01:00

sched/core: Fix NULL pointer access fault in sched_setaffinity() with non-SMP configs

The kernel commit 9a5418bc48ba ("sched/core: Use kfree_rcu() in
do_set_cpus_allowed()") introduces a bug for kernels built with non-SMP
configs. Calling sched_setaffinity() on such a uniprocessor kernel will
cause cpumask_copy() to be called with a NULL pointer leading to general
protection fault. This is not really a problem in real use cases as
there aren't that many uniprocessor kernel configs in use and calling
sched_setaffinity() on such a uniprocessor system doesn't make sense.

Fix this problem by making sure cpumask_copy() will not be called in
such a case.

Fixes: 9a5418bc48ba ("sched/core: Use kfree_rcu() in do_set_cpus_allowed()")
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
kernel/sched/core.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bb1ee6d..e838feb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8290,12 +8290,18 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
if (retval)
goto out_put_task;

+ /*
+ * With non-SMP configs, user_cpus_ptr/user_mask isn't used and
+ * alloc_user_cpus_ptr() returns NULL.
+ */
user_mask = alloc_user_cpus_ptr(NUMA_NO_NODE);
- if (IS_ENABLED(CONFIG_SMP) && !user_mask) {
+ if (user_mask) {
+ cpumask_copy(user_mask, in_mask);
+ } else if (IS_ENABLED(CONFIG_SMP)) {
retval = -ENOMEM;
goto out_put_task;
}
- cpumask_copy(user_mask, in_mask);
+
ac = (struct affinity_context){
.new_mask = in_mask,
.user_mask = user_mask,