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io_uring: grab task reference for poll requests 

We can have a task exit if it's not the owner of the ring. Be safe and
grab an actual reference to it, to avoid a potential use-after-free.

Reported-by: Dan Melnic <dmm@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2020-04-03 11:19:06 -06:00
parent a6ba632d2c
commit 3537b6a7c6
1 changed files with 7 additions and 12 deletions
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19
fs/io_uring.c
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@ -615,10 +615,8 @@ struct io_kiocb {
struct list_head list;
unsigned int flags;
refcount_t refs;
union {
struct task_struct *task;
unsigned long fsize;
};
struct task_struct *task;
unsigned long fsize;
u64 user_data;
u32 result;
u32 sequence;
@ -1336,6 +1334,7 @@ got_it:
req->flags = 0;
/* one is dropped after submission, the other at completion */
refcount_set(&req->refs, 2);
req->task = NULL;
req->result = 0;
INIT_IO_WORK(&req->work, io_wq_submit_work);
return req;
@ -1372,6 +1371,8 @@ static void __io_req_aux_free(struct io_kiocb *req)
kfree(req->io);
if (req->file)
io_put_file(req, req->file, (req->flags & REQ_F_FIXED_FILE));
if (req->task)
put_task_struct(req->task);
io_req_work_drop_env(req);
}
@ -4256,10 +4257,7 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
req->flags |= REQ_F_POLLED;
memcpy(&apoll->work, &req->work, sizeof(req->work));
/*
* Don't need a reference here, as we're adding it to the task
* task_works list. If the task exits, the list is pruned.
*/
get_task_struct(current);
req->task = current;
req->apoll = apoll;
INIT_HLIST_NODE(&req->hash_node);
@ -4482,10 +4480,7 @@ static int io_poll_add_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe
events = READ_ONCE(sqe->poll_events);
poll->events = demangle_poll(events) | EPOLLERR | EPOLLHUP;
/*
* Don't need a reference here, as we're adding it to the task
* task_works list. If the task exits, the list is pruned.
*/
get_task_struct(current);
req->task = current;
return 0;
}