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

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Date:	Tue, 02 Dec 2008 01:15:08 +0100
From:	Andi Kleen <ak@...ux.intel.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Jonathan Corbet <corbet@....net>,
	Al Viro <viro@...iv.linux.org.uk>,
	Vitaly Mayatskikh <vmayatsk@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: BUG? "Call fasync() functions without the BKL" is racy


> 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

>
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