linux-kernel - Re: WARNING in iov_iter

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Message-ID: <YDFlwf3AKbLiZhvh@zeniv-ca.linux.org.uk>
Date:   Sat, 20 Feb 2021 19:40:49 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     syzbot <syzbot+3d2c27c2b7dc2a94814d@...kaller.appspotmail.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-kernel@...r.kernel.org, snovitoll@...il.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: WARNING in iov_iter_revert (2)

On Sat, Feb 20, 2021 at 07:29:57PM +0000, Al Viro wrote:

> And then you notice that it has reports
> successful write of amount other than what you'd passed and tries
> to pull back.

Sorry, half-edited sentence has escaped ;-/  Should be

"And there the caller notices that callback has reported a successful
write, but the amount apparently written is not the same as the
amount it had asked to write.  It interprets that as a short write
and tries to pull back.  Only it's actually _forward_, since we'd
asked to write 0 bytes and got a small positive number from the
callback."