From 497f3fac6f3ed3ca78e485df41829c94661735a2 Mon Sep 17 00:00:00 2001
From: Jann Horn <jannh@google.com>
Date: Tue, 16 Jul 2019 17:20:45 +0200
Subject: [PATCH] sched/fair: Don't free p->numa_faults with concurrent
readers
Patch-mainline: v5.3-rc2
Git-commit: 16d51a590a8ce3befb1308e0e7ab77f3b661af33
References: bsc#1144920, bsc#1179663, CVE-2019-20934
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: Matt Fleming <mfleming@suse.de>
---
fs/exec.c | 2 +-
include/linux/sched/numa_balancing.h | 4 ++--
kernel/fork.c | 2 +-
kernel/sched/fair.c | 24 ++++++++++++++++++++----
4 files changed, 24 insertions(+), 8 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 04d473edbd1a..1eb10ef0792b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1795,7 +1795,7 @@ static int do_execveat_common(int fd, struct filename *filename,
current->fs->in_exec = 0;
current->in_execve = 0;
acct_update_integrals(current);
- task_numa_free(current);
+ task_numa_free(current, false);
free_bprm(bprm);
kfree(pathbuf);
putname(filename);
diff --git a/include/linux/sched/numa_balancing.h b/include/linux/sched/numa_balancing.h
index 35d5fc77b4be..fbb107f3afcd 100644
--- a/include/linux/sched/numa_balancing.h
+++ b/include/linux/sched/numa_balancing.h
@@ -18,7 +18,7 @@
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);
#else
@@ -33,7 +33,7 @@ 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 75ee3bcd22ff..11a880b869a9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -461,7 +461,7 @@ void __put_task_struct(struct task_struct *tsk)
WARN_ON(tsk == current);
cgroup_free(tsk);
- task_numa_free(tsk);
+ task_numa_free(tsk, true);
security_task_free(tsk);
exit_creds(tsk);
delayacct_tsk_free(tsk);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6df619254579..cdf90892937a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2347,13 +2347,23 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
return;
}
-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++)
@@ -2366,8 +2376,14 @@ void task_numa_free(struct task_struct *p)
put_numa_group(grp);
}
- 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;
+ }
}
/*
--
2.13.7