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| author | Qian Cai <cai@lca.pw> | 2020-03-30 17:30:02 -0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2020-04-08 12:05:06 +0200 |
| commit | d22cc7f67d55ebf2d5be865453971c783e9fb21a (patch) | |
| tree | 1330785754a3c2b269d797a9da763011e37e39ec /kernel | |
| parent | f5e94d10e4c468357019e5c28d48499f677b284f (diff) | |
| download | lwn-d22cc7f67d55ebf2d5be865453971c783e9fb21a.tar.gz lwn-d22cc7f67d55ebf2d5be865453971c783e9fb21a.zip | |
locking/percpu-rwsem: Fix a task_struct refcount
The following commit:
7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem")
introduced task_struct memory leaks due to messing up the task_struct
refcount.
At the beginning of percpu_rwsem_wake_function(), it calls get_task_struct(),
but if the trylock failed, it will remain in the waitqueue. However, it
will run percpu_rwsem_wake_function() again with get_task_struct() to
increase the refcount but then only call put_task_struct() once the trylock
succeeded.
Fix it by adjusting percpu_rwsem_wake_function() a bit to guard against
when percpu_rwsem_wait() observing !private, terminating the wait and
doing a quick exit() while percpu_rwsem_wake_function() then doing
wake_up_process(p) as a use-after-free.
Fixes: 7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200330213002.2374-1-cai@lca.pw
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/locking/percpu-rwsem.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c index a008a1ba21a7..8bbafe3e5203 100644 --- a/kernel/locking/percpu-rwsem.c +++ b/kernel/locking/percpu-rwsem.c @@ -118,14 +118,15 @@ static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode, int wake_flags, void *key) { - struct task_struct *p = get_task_struct(wq_entry->private); bool reader = wq_entry->flags & WQ_FLAG_CUSTOM; struct percpu_rw_semaphore *sem = key; + struct task_struct *p; /* concurrent against percpu_down_write(), can get stolen */ if (!__percpu_rwsem_trylock(sem, reader)) return 1; + p = get_task_struct(wq_entry->private); list_del_init(&wq_entry->entry); smp_store_release(&wq_entry->private, NULL); |