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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Dave Chinner <david@fromorbit.com>, CAI Qian <caiqian@redhat.com>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	xfs@oss.sgi.com, Jens Axboe <axboe@kernel.dk>,
	Nick Piggin <npiggin@gmail.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 10/12] new iov_iter flavour: pipe-backed
Date: Thu, 29 Sep 2016 23:50:03 +0100	[thread overview]
Message-ID: <20160929225003.GQ19539@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAELBmZDpm635PcTPQfnpLGs2P4bfT6JU+DEuFu9pBut=uzOLHw@mail.gmail.com>

On Thu, Sep 29, 2016 at 10:53:55PM +0200, Miklos Szeredi wrote:

> The EFAULT logic seems to be missing across the board.  And callers
> don't expect a zero return value.  Most will loop indefinitely.

Nope.  copy_page_to_iter() *never* returns -EFAULT.  Including the iovec
one - check copy_page_to_iter_iovec().  Any caller that does not expect
a zero return value from that primitive is a bug, triggerable as soon as
you feed it an iovec with NULL ->iov_base.

> Again, unexpected zero return if this is the first page.  Should
> return -ENOMEM?  Some callers only expect -EFAULT, though.

For copy_to_iter() and zero_iter() it's definitely "return zero".  For
get_pages...  Hell knows; those probably ought to return -EFAULT, but
I'll need to look some more at the callers.  It should end up triggering
a short read as the end result (or, as usual, EFAULT on zero-length read).

> > +               /* take it relative to the beginning of buffer */
> > +               size += off - pipe->bufs[idx].offset;
> > +               while (1) {
> > +                       buf = &pipe->bufs[idx];
> > +                       if (size > buf->len) {
> > +                               size -= buf->len;
> > +                               idx = next_idx(idx, pipe);
> > +                               off = 0;
> 
> off is unused and reassigned before breaking out of the loop.

True.

> [...]
> 
> > +       if (unlikely(i->type & ITER_PIPE)) {
> > +               struct pipe_inode_info *pipe = i->pipe;
> > +               size_t off;
> > +               int idx;
> > +
> > +               if (!sanity(i))
> > +                       return 0;
> > +
> > +               data_start(i, &idx, &off);
> > +               /* some of this one + all after this one */
> > +               npages = ((pipe->curbuf - idx - 1) & (pipe->buffers - 1)) + 1;
> 
> It's supposed to take i->count into account, no?  And that calculation
> will result in really funny things if the pipe is full.  And we can't
> return -EFAULT here, since that's not expected by callers...

It should look at i->count, in principle.  OTOH, overestimating the amount
is not really a problem for possible users of such iov_iter.  I'll look
into that.

  reply	other threads:[~2016-09-29 22:50 UTC|newest]

Thread overview: 104+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20160908235521.GL2356@ZenIV.linux.org.uk>
     [not found] ` <20160909015324.GD30056@dastard>
     [not found]   ` <CA+55aFzohsUXj_3BeFNr2t50Wm=G+7toRDEz=Tk7VJqP3n1hXQ@mail.gmail.com>
     [not found]     ` <CA+55aFxrqCng2Qxasc9pyMrKUGFjo==fEaFT1vkH9Lncte3RgQ@mail.gmail.com>
     [not found]       ` <20160909023452.GO2356@ZenIV.linux.org.uk>
     [not found]         ` <CA+55aFwHQMjO4-vtfB9-ytc=o+DRo-HXVGckvXLboUxgpwb7_g@mail.gmail.com>
     [not found]           ` <20160909221945.GQ2356@ZenIV.linux.org.uk>
     [not found]             ` <CA+55aFzTOOB6oEVaaGD0N7Uznk-W9+ULPwzsxS_L_oZqGVSeLA@mail.gmail.com>
     [not found]               ` <20160914031648.GB2356@ZenIV.linux.org.uk>
     [not found]                 ` <20160914133925.2fba4629@roar.ozlabs.ibm.com>
2016-09-18  5:33                   ` xfs_file_splice_read: possible circular locking dependency detected Al Viro
2016-09-19  3:08                     ` Nicholas Piggin
2016-09-19  6:11                       ` Al Viro
2016-09-19  7:26                         ` Nicholas Piggin
     [not found]                 ` <CA+55aFznQaOWoSMNphgGJJWZ=8-odrc0DAUMzfGPQe+_N4UgNA@mail.gmail.com>
     [not found]                   ` <20160914042559.GC2356@ZenIV.linux.org.uk>
     [not found]                     ` <20160917082007.GA6489@ZenIV.linux.org.uk>
     [not found]                       ` <20160917190023.GA8039@ZenIV.linux.org.uk>
2016-09-18 19:31                         ` skb_splice_bits() and large chunks in pipe (was " Al Viro
2016-09-18 20:12                           ` Linus Torvalds
2016-09-18 22:31                             ` Al Viro
2016-09-19  0:18                               ` Linus Torvalds
2016-09-19  0:22                               ` Al Viro
2016-09-20  9:51                                 ` Herbert Xu
2016-09-23 19:00                         ` [RFC][CFT] splice_read reworked Al Viro
2016-09-23 19:01                           ` [PATCH 01/11] fix memory leaks in tracing_buffers_splice_read() Al Viro
2016-09-23 19:02                           ` [PATCH 02/11] splice_to_pipe(): don't open-code wakeup_pipe_readers() Al Viro
2016-09-23 19:02                           ` [PATCH 03/11] splice: switch get_iovec_page_array() to iov_iter Al Viro
2016-09-23 19:03                           ` [PATCH 04/11] splice: lift pipe_lock out of splice_to_pipe() Al Viro
2016-09-23 19:45                             ` Linus Torvalds
2016-09-23 20:10                               ` Al Viro
2016-09-23 20:36                                 ` Linus Torvalds
2016-09-24  3:59                                   ` Al Viro
2016-09-24 17:29                                     ` Al Viro
2016-09-27 15:38                                       ` Nicholas Piggin
2016-09-27 15:53                                       ` Chuck Lever
2016-09-24  3:59                                   ` [PATCH 04/12] " Al Viro
2016-09-26 13:35                                     ` Miklos Szeredi
2016-09-27  4:14                                       ` Al Viro
2016-12-17 19:54                                     ` Andreas Schwab
2016-12-18 19:28                                       ` Linus Torvalds
2016-12-18 19:57                                         ` Andreas Schwab
2016-12-18 20:12                                         ` Al Viro
2016-12-18 20:30                                           ` Al Viro
2016-12-18 22:10                                             ` Linus Torvalds
2016-12-18 22:18                                               ` Al Viro
2016-12-18 22:22                                                 ` Linus Torvalds
2016-12-18 22:49                                               ` Andreas Schwab
2016-12-21 18:56                                               ` Andreas Schwab
2016-12-21 19:12                                                 ` Linus Torvalds
2016-09-24  4:00                                   ` [PATCH 06/12] new helper: add_to_pipe() Al Viro
2016-09-26 13:49                                     ` Miklos Szeredi
2016-09-24  4:01                                   ` [PATCH 10/12] new iov_iter flavour: pipe-backed Al Viro
2016-09-29 20:53                                     ` Miklos Szeredi
2016-09-29 22:50                                       ` Al Viro [this message]
2016-09-30  7:30                                         ` Miklos Szeredi
2016-10-03  3:34                                           ` [RFC] O_DIRECT vs EFAULT (was Re: [PATCH 10/12] new iov_iter flavour: pipe-backed) Al Viro
2016-10-03 17:07                                             ` Linus Torvalds
2016-10-03 18:54                                               ` Al Viro
2016-09-24  4:01                                   ` [PATCH 11/12] switch generic_file_splice_read() to use of ->read_iter() Al Viro
2016-09-24  4:02                                   ` [PATCH 12/12] switch default_file_splice_read() to use of pipe-backed iov_iter Al Viro
2016-09-23 19:03                           ` [PATCH 05/11] skb_splice_bits(): get rid of callback Al Viro
2016-09-23 19:04                           ` [PATCH 06/11] new helper: add_to_pipe() Al Viro
2016-09-23 19:04                           ` [PATCH 07/11] fuse_dev_splice_read(): switch to add_to_pipe() Al Viro
2016-09-23 19:06                           ` [PATCH 08/11] cifs: don't use memcpy() to copy struct iov_iter Al Viro
2016-09-23 19:08                           ` [PATCH 09/11] fuse_ioctl_copy_user(): don't open-code copy_page_{to,from}_iter() Al Viro
2016-09-26  9:31                             ` Miklos Szeredi
2016-09-23 19:09                           ` [PATCH 10/11] new iov_iter flavour: pipe-backed Al Viro
2016-09-23 19:10                           ` [PATCH 11/11] switch generic_file_splice_read() to use of ->read_iter() Al Viro
2016-09-30 13:32                           ` [RFC][CFT] splice_read reworked CAI Qian
2016-09-30 17:42                             ` CAI Qian
2016-09-30 18:33                               ` CAI Qian
2016-10-03  1:37                                 ` Al Viro
2016-10-03 17:49                                   ` CAI Qian
2016-10-04 17:39                                     ` local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT] splice_read reworked) CAI Qian
2016-10-04 21:42                                       ` tj
2016-10-05 14:09                                         ` CAI Qian
2016-10-05 15:30                                           ` tj
2016-10-05 15:54                                             ` CAI Qian
2016-10-05 18:57                                               ` CAI Qian
2016-10-05 20:05                                                 ` Al Viro
2016-10-06 12:20                                                   ` CAI Qian
2016-10-06 12:25                                                     ` CAI Qian
2016-10-06 16:11                                                       ` CAI Qian
2016-10-06 17:00                                                         ` Linus Torvalds
2016-10-06 18:12                                                           ` CAI Qian
2016-10-07  9:57                                                           ` Dave Chinner
2016-10-07 15:25                                                             ` Linus Torvalds
2016-10-07  7:08                                                       ` Jan Kara
2016-10-07 14:43                                                         ` CAI Qian
2016-10-07 15:27                                                           ` CAI Qian
2016-10-07 18:56                                                             ` CAI Qian
2016-10-09 21:54                                                               ` Dave Chinner
2016-10-10 14:10                                                                 ` CAI Qian
2016-10-10 20:14                                                                   ` CAI Qian
2016-10-10 21:57                                                                   ` Dave Chinner
2016-10-12 19:50                                                                     ` [bisected] " CAI Qian
2016-10-12 20:59                                                                       ` Dave Chinner
2016-10-13 16:25                                                                         ` CAI Qian
2016-10-13 20:49                                                                           ` Dave Chinner
2016-10-13 20:56                                                                             ` CAI Qian
2016-10-09 21:51                                                           ` Dave Chinner
2016-10-21 15:38                                                         ` [4.9-rc1+] overlayfs lockdep CAI Qian
2016-10-24 12:57                                                           ` Miklos Szeredi
2016-10-07  9:27                                                     ` local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT] splice_read reworked) Dave Chinner
2016-10-03  1:42                               ` [RFC][CFT] splice_read reworked Al Viro
2016-10-03 14:06                                 ` CAI Qian
2016-10-03 15:20                                   ` CAI Qian
2016-10-03 21:12                                     ` Dave Chinner
2016-10-04 13:57                                       ` CAI Qian
2016-10-03 20:32                                   ` CAI Qian
2016-10-03 20:35                                     ` Al Viro
2016-10-04 13:29                                       ` CAI Qian
2016-10-04 14:28                                         ` Al Viro
2016-10-04 16:21                                           ` CAI Qian
2016-10-04 20:12                                             ` Al Viro
2016-10-05 14:30                                               ` CAI Qian
2016-10-05 16:07                                                 ` Al Viro

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