From: Jens Axboe axboe@kernel.dk
[ Upstream commit 5e0e02f0d7e52cfc8b1adfc778dd02181d8b47b4 ]
futex_queue() -> __futex_queue() uses 'current' as the task to store in the struct futex_q->task field. This is fine for synchronous usage of the futex infrastructure, but it's not always correct when used by io_uring where the task doing the initial futex_queue() might not be available later on. This doesn't lead to any issues currently, as the io_uring side doesn't support PI futexes, but it does leave a potentially dangling pointer which is never a good idea.
Have futex_queue() take a task_struct argument, and have the regular callers pass in 'current' for that. Meanwhile io_uring can just pass in NULL, as the task should never be used off that path. In theory req->tctx->task could be used here, but there's no point populating it with a task field that will never be used anyway.
Reported-by: Jann Horn jannh@google.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Thomas Gleixner tglx@linutronix.de Link: https://lore.kernel.org/all/22484a23-542c-4003-b721-400688a0d055@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- io_uring/futex.c | 2 +- kernel/futex/core.c | 5 +++-- kernel/futex/futex.h | 11 ++++++++--- kernel/futex/pi.c | 2 +- kernel/futex/waitwake.c | 4 ++-- 5 files changed, 15 insertions(+), 9 deletions(-)
diff --git a/io_uring/futex.c b/io_uring/futex.c index e29662f039e1a..f108da4ff863c 100644 --- a/io_uring/futex.c +++ b/io_uring/futex.c @@ -349,7 +349,7 @@ int io_futex_wait(struct io_kiocb *req, unsigned int issue_flags) hlist_add_head(&req->hash_node, &ctx->futex_list); io_ring_submit_unlock(ctx, issue_flags);
- futex_queue(&ifd->q, hb); + futex_queue(&ifd->q, hb, NULL); return IOU_ISSUE_SKIP_COMPLETE; }
diff --git a/kernel/futex/core.c b/kernel/futex/core.c index ebdd76b4ecbba..3db8567f5a44e 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -532,7 +532,8 @@ void futex_q_unlock(struct futex_hash_bucket *hb) futex_hb_waiters_dec(hb); }
-void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb) +void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb, + struct task_struct *task) { int prio;
@@ -548,7 +549,7 @@ void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
plist_node_init(&q->list, prio); plist_add(&q->list, &hb->chain); - q->task = current; + q->task = task; }
/** diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h index 99b32e728c4ad..6b2f4c7eb720f 100644 --- a/kernel/futex/futex.h +++ b/kernel/futex/futex.h @@ -285,13 +285,15 @@ static inline int futex_get_value_locked(u32 *dest, u32 __user *from) }
extern void __futex_unqueue(struct futex_q *q); -extern void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb); +extern void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb, + struct task_struct *task); extern int futex_unqueue(struct futex_q *q);
/** * futex_queue() - Enqueue the futex_q on the futex_hash_bucket * @q: The futex_q to enqueue * @hb: The destination hash bucket + * @task: Task queueing this futex * * The hb->lock must be held by the caller, and is released here. A call to * futex_queue() is typically paired with exactly one call to futex_unqueue(). The @@ -299,11 +301,14 @@ extern int futex_unqueue(struct futex_q *q); * or nothing if the unqueue is done as part of the wake process and the unqueue * state is implicit in the state of woken task (see futex_wait_requeue_pi() for * an example). + * + * Note that @task may be NULL, for async usage of futexes. */ -static inline void futex_queue(struct futex_q *q, struct futex_hash_bucket *hb) +static inline void futex_queue(struct futex_q *q, struct futex_hash_bucket *hb, + struct task_struct *task) __releases(&hb->lock) { - __futex_queue(q, hb); + __futex_queue(q, hb, task); spin_unlock(&hb->lock); }
diff --git a/kernel/futex/pi.c b/kernel/futex/pi.c index d62cca5ed8f4c..635c7d5d42220 100644 --- a/kernel/futex/pi.c +++ b/kernel/futex/pi.c @@ -982,7 +982,7 @@ int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int tryl /* * Only actually queue now that the atomic ops are done: */ - __futex_queue(&q, hb); + __futex_queue(&q, hb, current);
if (trylock) { ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex); diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c index 3a10375d95218..a9056acb75eef 100644 --- a/kernel/futex/waitwake.c +++ b/kernel/futex/waitwake.c @@ -350,7 +350,7 @@ void futex_wait_queue(struct futex_hash_bucket *hb, struct futex_q *q, * access to the hash list and forcing another memory barrier. */ set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE); - futex_queue(q, hb); + futex_queue(q, hb, current);
/* Arm the timer */ if (timeout) @@ -461,7 +461,7 @@ int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *woken) * next futex. Queue each futex at this moment so hb can * be unlocked. */ - futex_queue(q, hb); + futex_queue(q, hb, current); continue; }