Re: [PATCH] x86/uaccess: small optimization in unsafe_copy_to_user()

From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Eric Dumazet <edumazet@google.com>, Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH] x86/uaccess: small optimization in unsafe_copy_to_user()
Date: Sat, 17 Apr 2021 20:35:18 +0000	[thread overview]
Message-ID: <YHtGhqBXhWlUHHRm@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <YHtFciNvBWYJ0ku2@zeniv-ca.linux.org.uk>

On Sat, Apr 17, 2021 at 08:30:42PM +0000, Al Viro wrote:

> and that thing is still there.  However, it does *NOT* do what it might
> appear to be doing; it ends up with getdents() returning -EINVAL instead.
> What we need is
> 			buf->error = -EINTR;
> in addition to that return (in all 3 such places).  Do you have any problems with
> the following delta?

No, wait - we have non-NULL buf->prev_reclen, so we'll hit
        if (buf.prev_reclen) {
		struct compat_linux_dirent __user * lastdirent;
		lastdirent = (void __user *)buf.current_dir - buf.prev_reclen;

		if (put_user(buf.ctx.pos, &lastdirent->d_off)) 
			error = -EFAULT;
		else
			error = count - buf.count;
	}
with buf->error completely ignored.  Nevermind.