Re: BUG? "Call fasync() functions without the BKL" is racy

Andi Kleen
2008-12-02T00:15:03Z

> Perhaps, we can add O_LOCK_FLAGS, then something like
>
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -175,6 +175,15 @@ static int setfl(int fd, struct file * f
> if (error)
> return error;
>
> + spin_lock(&current->files->file_lock);
> + if (!(filp->f_flags & O_LOCK_FLAGS))
> + filp->f_flags |= O_LOCK_FLAGS;
> + else
> + error = -EAGAIN;
> + spin_unlock(&current->files->file_lock);
> + if (error) /* pretend ->f_flags was changed after us */
> + return 0;
> +
> if ((arg ^ filp->f_flags) & FASYNC) {
> if (filp->f_op && filp->f_op->fasync) {
> error = filp->f_op->fasync(fd, filp, (arg & FASYNC) != 0);
> @@ -183,7 +192,8 @@ static int setfl(int fd, struct file * f
> }
> }
>
> - filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK);
> + filp->f_flags = (arg & SETFL_MASK) |
> + (filp->f_flags & ~(SETFL_MASK | O_LOCK_FLAGS));
> out:
> return error;
> }
>
> What do you think?

Looks reasonable. Just would need to make sure that O_LOCK_FLAGS doesn't
leak out to user space.

-Andi

>