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From: Bart Van Assche <bvanassche@acm.org>
To: Bodo Stroesser <bostroesser@gmail.com>, Christoph Hellwig <hch@lst.de>
Cc: Joel Becker <jlbec@evilplan.org>,
	linux-kernel@vger.kernel.org,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	Yanko Kaneti <yaneti@declera.com>,
	Brendan Higgins <brendanhiggins@google.com>
Subject: Re: [PATCH 2/4] configfs: Fix writing at a non-zero offset
Date: Tue, 27 Jul 2021 09:47:24 -0700	[thread overview]
Message-ID: <a3ba73e5-ffd1-887e-acd9-11f537db27e0@acm.org> (raw)
In-Reply-To: <fec30933-46b1-1085-1af1-1fd0d2265981@gmail.com>

On 7/27/21 12:27 AM, Bodo Stroesser wrote:
> What I meant is, that changing the source code in such a way, that
> writing a buffer in multiple writes works in general, could cause
> trouble in case userspace uses this.
> 
> But for special syscall sequences your changes still change the result
> on existing configfs files. Example:
> 
> 1) userspace program opens qfull_time_out
> 2) userspace program writes "90", count=2 to set timeout to 90 sec
> 3) userspace again wants to change timeout, so it writes "55", count=2
> 
> Before the changes we end up with timeout being 55 seconds. After the
> change - due to data gathering - we finally have timeout 9055 seconds.

Hi Bodo,

How about replacing patches 1 and 2 from this series with the patch below?
Do you agree that this patch is sufficient to restore the behavior from
kernel v5.13 and before?

Thanks,

Bart.

Subject: [PATCH 1/3] configfs: Restore the kernel v5.13 text attribute write behavior

Instead of writing at the offset specified by the write() system call,
always write at offset zero.

Cc: Bodo Stroesser <bostroesser@gmail.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Yanko Kaneti <yaneti@declera.com>
Cc: Brendan Higgins <brendanhiggins@google.com>
Reported-by: Bodo Stroesser <bostroesser@gmail.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
  fs/configfs/file.c | 20 ++++++++------------
  1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/fs/configfs/file.c b/fs/configfs/file.c
index 5a0be9985bae..8adf6250b207 100644
--- a/fs/configfs/file.c
+++ b/fs/configfs/file.c
@@ -177,12 +177,11 @@ static ssize_t configfs_bin_read_iter(struct kiocb *iocb, struct iov_iter *to)
  	return retval;
  }

-/* Fill [buffer, buffer + pos) with data coming from @from. */
-static int fill_write_buffer(struct configfs_buffer *buffer, loff_t pos,
+/* Fill @buffer with data coming from @from. */
+static int fill_write_buffer(struct configfs_buffer *buffer,
  			     struct iov_iter *from)
  {
-	loff_t to_copy;
-	int copied;
+	int to_copy, copied;
  	u8 *to;

  	if (!buffer->page)
@@ -190,11 +189,8 @@ static int fill_write_buffer(struct configfs_buffer *buffer, loff_t pos,
  	if (!buffer->page)
  		return -ENOMEM;

-	to_copy = SIMPLE_ATTR_SIZE - 1 - pos;
-	if (to_copy <= 0)
-		return 0;
-	to = buffer->page + pos;
-	copied = copy_from_iter(to, to_copy, from);
+	to = buffer->page;
+	copied = copy_from_iter(to, SIMPLE_ATTR_SIZE - 1, from);
  	buffer->needs_read_fill = 1;
  	/* if buf is assumed to contain a string, terminate it by \0,
  	 * so e.g. sscanf() can scan the string easily */
@@ -227,14 +223,14 @@ static ssize_t configfs_write_iter(struct kiocb *iocb, struct iov_iter *from)
  {
  	struct file *file = iocb->ki_filp;
  	struct configfs_buffer *buffer = file->private_data;
-	ssize_t len;
+	int len;

  	mutex_lock(&buffer->mutex);
-	len = fill_write_buffer(buffer, iocb->ki_pos, from);
+	len = fill_write_buffer(buffer, from);
  	if (len > 0)
  		len = flush_write_buffer(file, buffer, len);
  	if (len > 0)
-		iocb->ki_pos += len;
+		iocb->ki_pos = len;
  	mutex_unlock(&buffer->mutex);
  	return len;
  }

  reply	other threads:[~2021-07-27 16:47 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-23 21:23 [PATCH 0/4] Improve the configfs read and write iterators further Bart Van Assche
2021-07-23 21:23 ` [PATCH 1/4] configfs: Rework the overflow check in fill_write_buffer() Bart Van Assche
2021-07-23 21:23 ` [PATCH 2/4] configfs: Fix writing at a non-zero offset Bart Van Assche
2021-07-26 14:58   ` Bodo Stroesser
2021-07-26 16:26     ` Bart Van Assche
2021-07-26 21:13       ` Bodo Stroesser
2021-07-26 21:52         ` Bart Van Assche
2021-07-27  0:54           ` Bodo Stroesser
2021-07-27  3:17             ` Bart Van Assche
2021-07-27  7:27               ` Bodo Stroesser
2021-07-27 16:47                 ` Bart Van Assche [this message]
2021-07-28 17:14                   ` Bodo Stroesser
2021-07-28 17:55                     ` Bart Van Assche
2021-07-23 21:23 ` [PATCH 3/4] kunit: Add support for suite initialization and cleanup Bart Van Assche
2021-07-27 21:26   ` Brendan Higgins
2021-07-29  3:33     ` Bart Van Assche
2021-07-23 21:23 ` [PATCH 4/4] configfs: Add unit tests Bart Van Assche

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