linux-kernel - Re: [PATCH] x86/uaccess: small optimization in unsafe_copy_to

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Message-ID: <YHtGhqBXhWlUHHRm@zeniv-ca.linux.org.uk>
Date:   Sat, 17 Apr 2021 20:35:18 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH] x86/uaccess: small optimization in unsafe_copy_to_user()

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.