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sched/fair: Don't free p->numa_faults with concurrent readers

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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: 82727018b0 ("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>
This commit is contained in:
Jann Horn 2019-07-16 17:20:45 +02:00 committed by Ingo Molnar
parent 7b5cf701ea
commit 16d51a590a
4 changed files with 24 additions and 8 deletions
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2
fs/exec.c
View File

@ -1828,7 +1828,7 @@ static int __do_execve_file(int fd, struct filename *filename,
membarrier_execve(current);
rseq_execve(current);
acct_update_integrals(current);
task_numa_free(current);
task_numa_free(current, false);
free_bprm(bprm);
kfree(pathbuf);
if (filename)

4
include/linux/sched/numa_balancing.h
View File

@ -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);
#else
@ -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,

2
kernel/fork.c
View File

@ -726,7 +726,7 @@ 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);

24
kernel/sched/fair.c
View File

@ -2353,13 +2353,23 @@ 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++)
@ -2372,8 +2382,14 @@ 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;
}
}
/*