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authorJann Horn <jannh@google.com>2019-07-16 17:20:45 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-08-04 09:32:03 +0200
commitd0919216e468d5613cc8c53d4d0676026960fe39 (patch)
parent69f9c2bc3f754ad1d610b30b940681d678c8e684 (diff)
sched/fair: Don't free p->numa_faults with concurrent readers
commit 16d51a590a8ce3befb1308e0e7ab77f3b661af33 upstream. When going through execve(), zero out the NUMA fault statistics instead of freeing them. During execve, the task is reachable through procfs and the scheduler. A concurrent /proc/*/sched reader can read data from a freed ->numa_faults allocation (confirmed by KASAN) and write it back to userspace. I believe that it would also be possible for a use-after-free read to occur through a race between a NUMA fault and execve(): task_numa_fault() can lead to task_numa_compare(), which invokes task_weight() on the currently running task of a different CPU. Another way to fix this would be to make ->numa_faults RCU-managed or add extra locking, but it seems easier to wipe the NUMA fault statistics on execve. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Petr Mladek <pmladek@suse.com> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will@kernel.org> Fixes: 82727018b0d3 ("sched/numa: Call task_numa_free() from do_execve()") Link: https://lkml.kernel.org/r/20190716152047.14424-1-jannh@google.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
4 files changed, 24 insertions, 8 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 0936b5a8199a..4623fc3ac86b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1808,7 +1808,7 @@ static int do_execveat_common(int fd, struct filename *filename,
current->in_execve = 0;
- task_numa_free(current);
+ task_numa_free(current, false);
diff --git a/include/linux/sched/numa_balancing.h b/include/linux/sched/numa_balancing.h
index e7dd04a84ba8..3988762efe15 100644
--- a/include/linux/sched/numa_balancing.h
+++ b/include/linux/sched/numa_balancing.h
@@ -19,7 +19,7 @@
extern void task_numa_fault(int last_node, int node, int pages, int flags);
extern pid_t task_numa_group_id(struct task_struct *p);
extern void set_numabalancing_state(bool enabled);
-extern void task_numa_free(struct task_struct *p);
+extern void task_numa_free(struct task_struct *p, bool final);
extern bool should_numa_migrate_memory(struct task_struct *p, struct page *page,
int src_nid, int dst_cpu);
@@ -34,7 +34,7 @@ static inline pid_t task_numa_group_id(struct task_struct *p)
static inline void set_numabalancing_state(bool enabled)
-static inline void task_numa_free(struct task_struct *p)
+static inline void task_numa_free(struct task_struct *p, bool final)
static inline bool should_numa_migrate_memory(struct task_struct *p,
diff --git a/kernel/fork.c b/kernel/fork.c
index a5bb8fad5475..919e7cd5cd23 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -415,7 +415,7 @@ void __put_task_struct(struct task_struct *tsk)
WARN_ON(tsk == current);
- task_numa_free(tsk);
+ task_numa_free(tsk, true);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index af7de1f9906c..0a4e882d4308 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2358,13 +2358,23 @@ no_join:
-void task_numa_free(struct task_struct *p)
+ * Get rid of NUMA staticstics associated with a task (either current or dead).
+ * If @final is set, the task is dead and has reached refcount zero, so we can
+ * safely free all relevant data structures. Otherwise, there might be
+ * concurrent reads from places like load balancing and procfs, and we should
+ * reset the data back to default state without freeing ->numa_faults.
+ */
+void task_numa_free(struct task_struct *p, bool final)
struct numa_group *grp = p->numa_group;
- void *numa_faults = p->numa_faults;
+ unsigned long *numa_faults = p->numa_faults;
unsigned long flags;
int i;
+ if (!numa_faults)
+ return;
if (grp) {
spin_lock_irqsave(&grp->lock, flags);
for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
@@ -2377,8 +2387,14 @@ void task_numa_free(struct task_struct *p)
- p->numa_faults = NULL;
- kfree(numa_faults);
+ if (final) {
+ p->numa_faults = NULL;
+ kfree(numa_faults);
+ } else {
+ p->total_numa_faults = 0;
+ for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
+ numa_faults[i] = 0;
+ }