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From:   Sabyrzhan Tasbolatov <snovitoll@gmail.com>
To:     torvalds@linux-foundation.org
Cc:     gregkh@linuxfoundation.org, jirislaby@kernel.org,
        linux-kernel@vger.kernel.org,
        syzbot+3d2c27c2b7dc2a94814d@syzkaller.appspotmail.com,
        syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk
Subject: Re: WARNING in iov_iter_revert (2)
Date:   Sun, 21 Feb 2021 14:37:05 +0600
Message-Id: <20210221083705.3075978-1-snovitoll@gmail.com>
In-Reply-To: <CAHk-=wgJuiASyuFSBR9GgN2iPSL7Ep7G_GR1kKsGTL=qhDTDUg@mail.gmail.com>
References: <CAHk-=wgJuiASyuFSBR9GgN2iPSL7Ep7G_GR1kKsGTL=qhDTDUg@mail.gmail.com>
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>    --- a/drivers/tty/tty_io.c
>    +++ b/drivers/tty/tty_io.c
>    @@ -961,6 +961,9 @@ static inline ssize_t do_tty_write(
>                 ret = write(tty, file, tty->write_buf, size);
>                 if (ret <= 0)
>                         break;
>    +            /* ttyprintk historical oddity */
>    +            if (ret > size)
>    +                    break;
> 
>                 /* FIXME! Have Al check this! */
>                 if (ret != size)
> 
> in there. Because right now we clearly do strange and not-so-wonderful
> things if the write routine returns a bigger value than it was
> passed.. Not limited to that iov_iter_revert() thing, but the whole
> loop.
> 
> Comments?

Just want to comment that this fix is correct (tested),
rather than what I did [1] to return abruptly
in the beginning of do_tty_write() for write(fd, NULL, 0) case.

Let me know if I can prepare a patch with Linus's fix above.

[1] https://lore.kernel.org/lkml/20210217155536.2986178-1-snovitoll@gmail.com
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -905,6 +905,9 @@ static inline ssize_t do_tty_write(
 	ssize_t ret, written = 0;
 	unsigned int chunk;
 
+	if (!count)
+		return -EFAULT;
+
 	ret = tty_write_lock(tty, file->f_flags & O_NDELAY);
 	if (ret < 0)
 		return ret;