On Wed, Feb 8, 2017 at 4:00 PM, Sahitya Tummala <stummala@xxxxxxxxxxxxxx> wrote:
> There is a potential race between fuse_dev_do_write()
> and request_wait_answer() contexts as shown below:
>
> TASK 1:
> __fuse_request_send():
> |--spin_lock(&fiq->waitq.lock);
> |--queue_request();
> |--spin_unlock(&fiq->waitq.lock);
> |--request_wait_answer():
> |--if (test_bit(FR_SENT, &req->flags))
> <gets pre-empted after it is validated true> TASK 2:
> fuse_dev_do_write():
> |--clears bit FR_SENT,
> |--request_end():
> |--sets bit FR_FINISHED
> |--spin_lock(&fiq->waitq.lock);
> |--list_del_init(&req->intr_entry);
> |--spin_unlock(&fiq->waitq.lock);
> |--fuse_put_request();
> |--queue_interrupt();
> <request gets queued to interrupts list>
> |--wake_up_locked(&fiq->waitq);
> |--wait_event_freezable();
> <as FR_FINISHED is set, it returns and then
> the caller frees this request>
>
> Now, the next fuse_dev_do_read(), see interrupts list is not empty
> and then calls fuse_read_interrupt() which tries to access the request
> which is already free'd and gets the below crash:
>
> [11432.401266] Unable to handle kernel paging request at virtual address
> 6b6b6b6b6b6b6b6b
> ...
> [11432.418518] Kernel BUG at ffffff80083720e0
> [11432.456168] PC is at __list_del_entry+0x6c/0xc4
> [11432.463573] LR is at fuse_dev_do_read+0x1ac/0x474
> ...
> [11432.679999] [<ffffff80083720e0>] __list_del_entry+0x6c/0xc4
> [11432.687794] [<ffffff80082c65e0>] fuse_dev_do_read+0x1ac/0x474
> [11432.693180] [<ffffff80082c6b14>] fuse_dev_read+0x6c/0x78
> [11432.699082] [<ffffff80081d5638>] __vfs_read+0xc0/0xe8
> [11432.704459] [<ffffff80081d5efc>] vfs_read+0x90/0x108
> [11432.709406] [<ffffff80081d67f0>] SyS_read+0x58/0x94
>
> As FR_FINISHED bit is set before deleting the intr_entry with input
> queue lock in request completion path, do the testing of this flag and
> queueing atomically with the same lock in queue_interrupt().
Thanks, fix added to 4.10.
Miklos
>
> Signed-off-by: Sahitya Tummala <stummala@xxxxxxxxxxxxxx>
> ---
> fs/fuse/dev.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 4e06a27..b656e18 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -399,6 +399,10 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
> static void queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
> {
> spin_lock(&fiq->waitq.lock);
> + if (test_bit(FR_FINISHED, &req->flags)) {
> + spin_unlock(&fiq->waitq.lock);
> + return;
> + }
> if (list_empty(&req->intr_entry)) {
> list_add_tail(&req->intr_entry, &fiq->interrupts);
> wake_up_locked(&fiq->waitq);
> --
> Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
>
